Señales de tráficoPolonia

A traffic mirror is a convex roadside mirror that helps road users see around an obstruction or into a road with limited visibility.

They may be placed near intersections, narrow roads, bends, car-park exits, private driveways, tunnels or other locations where buildings, vegetation or road geometry obstruct the view.

A convex surface provides a wider field of view than a flat mirror, allowing more of the approaching road to be seen.

No. The reflected image is distorted, and objects normally appear smaller and farther away than they really are.

Not reliably. The curved image makes it difficult to estimate how fast another road user is approaching.

No. Distance can appear greater than it really is, so an approaching vehicle may reach the intersection sooner than expected.

Yes. Its position and viewing angle may leave parts of the road outside the reflected image. Small cyclists, motorcycles or pedestrians may also be difficult to notice.

No. It does not change priority. Drivers must continue to follow stop signs, give-way signs, traffic lights and the ordinary priority rules.

No. Another road user may be outside the reflected area, hidden by glare or too small to notice. Always check the road directly before proceeding.

Yes. The mirror does not replace the mandatory complete stop. Stop at the prescribed position, then use direct observation and the mirror as additional information.

Yes. You may proceed only when traffic with priority can continue without being forced to brake, stop or change direction.

Approach slowly, stop when required and scan the mirror for movement. Then look directly in both directions and continue only after confirming that the road is clear.

No. Alternate between the mirror and direct observation. The mirror should supplement rather than replace normal checks.

Yes. Rain, water droplets and spray may blur or partially obscure the reflected image.

Yes. Dew, condensation, frost, ice or snow may make the mirror difficult or impossible to use.

Yes. Sunlight may create glare or reflections that hide approaching road users.

Yes. Reflected headlights may make it difficult to determine the exact direction, distance or speed of an approaching vehicle.

Yes. Wind, impacts, vandalism, vibration or temperature changes may alter its orientation and make the reflected view inaccurate.

Do not rely on it. Proceed with additional caution and report the defect to the responsible road authority or property owner.

No. The applicable road or posted speed limit remains in force, but restricted visibility normally requires a lower approach speed.

No. Use the horn only where local law permits it and a warning is reasonably necessary to prevent danger.

Yes. It may help them observe approaching traffic, but they must also look directly and follow the applicable crossing and priority rules.

A mirror may generally be installed on private property with the owner’s permission, subject to local rules. Installing one on, above or beside a public road normally requires permission from the road authority.

No. Removing vegetation, relocating parking, improving the intersection layout or changing traffic circulation may provide a safer and more reliable solution.

An international border is the legal boundary between two countries.

It may be identified by a country-name sign, national or regional symbols, flags, border posts, customs facilities or passport-control signs.

No. Borders may be marked differently, and some minor roads or open-border areas may have only a small identification sign or boundary marker.

Not normally. Stop only when required by traffic lights, barriers, officers, customs signs, passport controls or another instruction.

The new country’s traffic laws apply from the international boundary, not merely from the next town or major intersection.

No. The rules change because you have entered another country. The sign identifies that change of jurisdiction.

Yes. Where neighbouring countries use different driving sides, a specially designed road arrangement guides traffic safely from one side to the other.

Yes. The destination country may have different general limits for motorways, built-up areas, rural roads and particular vehicle categories.

No. Drivers must learn the destination country’s general limits and obey any regulatory signs displayed after crossing.

Yes. Colours, symbols, shapes and road-marking conventions may differ, even when neighbouring countries follow similar international standards.

Yes. Requirements concerning safety vests, warning triangles, winter tyres, lights, toll equipment or environmental stickers may differ between countries.

Depending on the journey, drivers may need a passport or identity card, driving licence, vehicle-registration document, insurance evidence, visa or customs documents.

No. Border or immigration control concerns people and travel documents. Customs control principally concerns goods, cargo, money and applicable duties or restrictions.

Yes. Both may operate at the same border facility even though they perform different legal functions.

No. Countries participating in an open-border area may normally cross internal borders without routine checks, although temporary controls may still be introduced.

No. Countries within a customs union may allow goods to move across their internal borders without ordinary customs duties or routine customs formalities.

No. Police, customs and other authorities may still conduct lawful checks, enforce national rules and temporarily control the border where permitted.

Only where local law permits it. External or controlled borders may have to be crossed through an authorised border-crossing point during its operating hours.

Yes. Closures or restrictions may result from security measures, emergencies, severe weather, roadworks or administrative decisions.

Yes. A crossing may restrict heavy vehicles, dangerous goods, agricultural traffic, pedestrians or cyclists because of road design or border-control facilities.

Yes. Commercial goods, restricted products, goods exceeding personal allowances and certain amounts of cash may require declaration.

They may. The destination country may use toll roads, vignettes, distance-based charges, low-emission zones or other payment systems.

No. Navigation information may not include current border controls, vehicle restrictions or document requirements. Follow official signs and instructions.

Check the destination and transit countries’ traffic rules, required documents, insurance, vehicle equipment, tolls and border or customs requirements.

Yes. Follow lawful instructions from authorised border, police and customs officers, even when they temporarily differ from the normal traffic arrangement.

A pedestrian underpass is a passage that allows pedestrians to cross beneath a road, railway or other obstacle without entering the traffic route above.

They separate pedestrians from motor vehicles, trains or other traffic, reducing direct conflicts at busy or high-speed crossings.

Not exactly. A pedestrian underpass is specifically intended to allow pedestrians to pass beneath an obstacle, while a tunnel can carry roads, railways, pedestrians or other forms of transport.

No. An underpass passes beneath the obstacle, while an overpass or footbridge carries pedestrians above it. Both provide grade-separated crossings.

This depends on the signs and design of the facility. Some underpasses are shared with cyclists, while pedestrian-only underpasses may require cyclists to dismount.

Yes. Some underpasses contain separate or shared pedestrian and cycle facilities so both categories can cross safely away from motor traffic.

No when the passage is specifically reserved for pedestrians. Maintenance or emergency access may be permitted in exceptional circumstances.

Yes, when suitably designed. Ramps or lifts can provide step-free access, although accessibility depends on the individual facility.

Yes. Users must follow any signs indicating permitted users, direction of travel, separated sections or temporary closures.

Yes. Maintenance, flooding, construction, safety concerns or other circumstances may require temporary closure or diversion.

The underpass physically separates the movements, so pedestrians do not directly cross the traffic route above. Priority rules still apply wherever the pedestrian route later crosses another roadway or cycle facility.

Where cycling is not permitted, cyclists should dismount and continue on foot if pedestrian access with a bicycle is allowed.

Cycling routes are commonly indicated by direction signs, bicycle symbols, route numbers, colours or destination markers. The design of the signs and route-numbering system varies between countries and regions.

Usually not. A cycling-route sign normally provides direction or route guidance rather than imposing a mandatory direction. However, separate mandatory traffic signs may require cyclists to use a particular cycle path or direction.

No. A cycle path is a specific part of a road or separate path intended for cyclists under local traffic rules. A cycling route is an entire itinerary and may include cycle paths, ordinary roads, cycle streets and other types of infrastructure.

Not necessarily. Many cycling routes use roads and paths that are also open to motor vehicles, pedestrians or other road users. Access is determined by the signs and rules applying to each individual section.

Not automatically. Being on a designated cycling route does not normally change the priority rules. Cyclists must continue to obey traffic lights, give-way and stop signs, crossing rules and other applicable traffic regulations.

No. A route may combine dedicated cycle infrastructure with quiet streets, shared roads, rural roads and other suitable connections. The quality and level of separation from motor traffic can therefore change along the route.

Yes. A cycling route may cross or temporarily follow busy roads. At such locations, cyclists must follow the crossing, priority and traffic-light rules indicated by local signs and markings.

Yes, unless access is restricted by separate traffic signs or regulations. A cycling-route designation by itself does not normally prohibit cars, motorcycles or other vehicles from using an otherwise public road.

Yes. Cycling routes may be designed for daily travel, tourism or recreation. Some form part of regional, national or international networks and may be identified by route names or numbers.

Always follow the official traffic signs, signals and road markings. A route marker provides navigation and does not override a prohibition, mandatory direction, road closure or other traffic regulation.

Parking generally means leaving a vehicle stationary for longer than a brief stop required for passengers, loading or unloading. A vehicle stopped because of traffic lights, congestion, an emergency or another traffic condition is normally not considered parked. The precise legal definitions vary between countries.

Look for parking signs, prohibition signs, road markings and parking-zone signs. Local rules may also permit parking along certain roads even when individual parking spaces are not marked.

No. General traffic rules can prohibit parking even when no specific prohibition sign is present. Common examples include locations where a parked vehicle would obstruct visibility, crossings, intersections, cycle facilities or the movement of other traffic.

Parking on a pavement or sidewalk is prohibited or restricted in many countries unless signs or markings specifically allow it. Vehicles must not force pedestrians into the roadway or block an accessible pedestrian route.

Parking on or close to a pedestrian crossing is generally restricted because a vehicle can hide pedestrians from approaching drivers. The required clearance distance varies between countries.

Many countries prohibit parking within a specified distance of an intersection because parked vehicles can reduce visibility and obstruct turning traffic. Follow the local distance requirements and any signs or markings.

A parking sign identifies a place or area where parking is permitted or regulated. Additional signs or panels may specify time limits, payment requirements, vehicle categories, permits or particular parking arrangements.

Where parking is subject to payment, drivers must follow the instructions displayed locally. Payment may be made through a parking meter, ticket machine, mobile application or another authorised system. The permitted duration and charging periods vary by location.

Spaces marked for people with disabilities are reserved for vehicles displaying or registered with the required disability parking permit. Eligibility, permit display requirements and parking privileges depend on national and local law.

Not necessarily. Local rules may impose a maximum parking duration, even where parking is otherwise permitted. Different limits may apply to abandoned, commercial, heavy or recreational vehicles.

A no-parking sign prohibits leaving a vehicle parked in the area or along the section of road to which the restriction applies. The exact legal definition of parking and the extent of the prohibition vary between countries.

No. A no-parking restriction commonly still permits certain brief stops, such as picking up or dropping off passengers or loading or unloading goods. A no-stopping restriction is stricter and generally prohibits voluntary stopping as well as parking.

Remaining inside the vehicle does not necessarily mean that it is not parked. If the vehicle remains stationary beyond what local law permits as a brief stop, it may legally be considered parked even when the driver stays inside.

Often yes, if stopping is permitted and the vehicle remains there only as long as reasonably necessary for passengers to get in or out. Local rules may impose stricter restrictions at particular locations.

In many countries, genuine loading or unloading is treated as stopping rather than parking and may therefore be permitted. The vehicle should remain there only for the time reasonably necessary for the activity.

This depends on the country's signing rules. The restriction may continue to the next intersection, an end sign, a stated distance or the end of a designated zone. Supplementary arrows or distance panels may indicate its exact extent.

Usually a roadside no-parking sign applies only to the side of the road on which it is placed, unless it forms part of a zonal restriction or local signs indicate otherwise.

Yes. A supplementary panel may restrict the prohibition to particular hours, days or periods. Outside those periods, parking may be permitted if no other rule prohibits it.

Yes. Additional signs or symbols may make a parking restriction applicable to particular vehicle categories, such as heavy vehicles, motorcycles or other specified vehicles.

Only if parking is otherwise legal. The end of a specific no-parking restriction does not override general parking prohibitions near crossings, intersections, driveways, traffic signs or other protected locations.

It means that a driver may not voluntarily stop the vehicle in the restricted area. The prohibition normally includes stopping to pick up or drop off passengers or to load or unload goods.

No stopping is the stricter restriction. A no-parking rule may still allow a brief stop for activities such as picking up passengers or loading goods, while a no-stopping rule prohibits these voluntary stops as well.

A driver may have to stop because of an emergency, traffic conditions, a red light, police instructions or another situation outside the driver's control. Such compulsory stops are generally different from voluntarily stopping the vehicle.

P+R stands for park and ride. It indicates a facility where drivers can park their vehicle and continue their journey using public transport or another form of transport.

They are commonly located on the outskirts of cities, near major roads or beside railway, metro, tram or bus connections so that drivers can transfer conveniently to another mode of transport.

No. Some facilities are free, while others charge for parking or offer special combined parking and public-transport fares. Conditions depend on the individual facility and local authority.

A Kiss and Ride area is a designated place where drivers can briefly stop to drop off or pick up passengers. It is intended to keep passenger transfers quick and reduce unnecessary parking or congestion near busy destinations.

Normally no. Kiss and Ride areas are intended for immediate passenger drop-off or pick-up rather than ordinary parking. The exact legal restrictions depend on the signs and local regulations applying to the area.

Generally, you should not remain in the area waiting for a passenger who is not ready to enter the vehicle. If waiting is necessary, use an ordinary parking or waiting area unless local signs specifically permit waiting.

Only for the short period necessary for passengers to get in or out, unless signs specify a particular maximum time. Some locations establish an explicit time limit, while others simply require immediate drop-off or pick-up.

Where possible, the driver should normally remain ready to move the vehicle immediately. Leaving the vehicle to accompany a passenger into a building may turn the stop into parking and can prevent other drivers from using the area efficiently.

Passengers may normally take the luggage they need when entering or leaving the vehicle, provided this forms part of the immediate passenger transfer. Using the area for prolonged loading or unloading may not be permitted.

They are frequently located near schools, railway stations, airports, hospitals and other busy destinations where many passengers are dropped off or collected within a short period.

This depends on the local signs and regulations. A general passenger drop-off area may be available to taxis, while some locations provide separate taxi ranks or reserve the Kiss and Ride area for particular users.

Normally this should be avoided. Kiss and Ride areas are designed for rapid passenger transfers, and leaving the vehicle unattended can obstruct other users. Specific local rules may expressly prohibit parking or unattended vehicles.

Move to a suitable parking or waiting area and return when the passenger is ready to be collected. Remaining in the Kiss and Ride area unnecessarily can block the facility and contribute to congestion.

Disabled parking spaces are intended for eligible people who hold a valid disabled parking permit or card. The exact eligibility requirements and permit system depend on the country.

Generally no. Disabled parking permits are normally personal and may only be used when the permit holder is driving or travelling in the vehicle.

No. A permit may provide access to reserved spaces or exemptions from certain parking restrictions, but rules concerning parking charges and time limits vary between countries and local authorities.

Traffic management is the organised control and guidance of traffic using signs, signals, road markings, lane controls, speed restrictions, diversions and other measures.

Traffic management is used to improve safety, control traffic flow and reduce disruption. It can also protect road workers, pedestrians, cyclists and emergency services.

Common methods include traffic lights, road signs, road markings, variable-message signs, lane-control signals, temporary barriers, speed restrictions and diversions. Authorised persons may also direct traffic.

Yes. Temporary or variable speed-limit signs may impose a different maximum speed because of congestion, roadworks, weather, incidents or other conditions. Drivers must follow the limit currently displayed.

Yes. Lane-control signals, temporary signs or road markings may close lanes, move traffic into different lanes or require drivers to change lane. Follow the current signs and markings rather than the normal road layout.

Move into an open lane safely and in good time, following any arrows, signs and local merging rules. Never continue along a lane that is clearly indicated as closed.

Yes. Properly authorised temporary signs used for roadworks, incidents or other traffic-management measures must be obeyed in the same way as other official traffic signs.

Follow the directions of the authorised person. In many countries, these directions take precedence over traffic lights, road signs or the normal traffic rules.

Roadworks may use temporary speed limits, lane closures, barriers, temporary markings, traffic lights and diversions. Road users should reduce speed where necessary and carefully follow the temporary route.

Yes. Temporary or permanent traffic arrangements should account for pedestrians and cyclists as well as motor vehicles. They may be provided with separate routes, crossings, signals or diversions where necessary.

Merging means joining another stream or lane of traffic, usually where an entry lane, acceleration lane or another traffic lane connects with the continuing roadway.

This depends on the road layout and national traffic rules. In many situations, the driver changing lanes must give way to vehicles already travelling in the lane being entered, unless signs or specific merging rules provide otherwise.

Zipper merging is a system used where a lane ends during congested traffic. Drivers use both lanes up to the merging point and then enter the continuing lane alternately, one vehicle from each traffic stream.

Check behind and around the vehicle for pedestrians, cyclists, other vehicles and obstacles. Use mirrors and cameras where available, but also look directly because monitoring systems can have blind spots.

In many countries, reversing is treated as a manoeuvre and the reversing driver must give way to other road users. The exact legal requirements depend on national traffic rules.

No. Reversing should normally be limited to the distance necessary to complete the manoeuvre safely. Driving forward generally provides better visibility and vehicle control.

A U-turn is a manoeuvre used to reverse a vehicle's direction so that it continues along the road in the opposite direction.

Check traffic in all relevant directions, mirrors and blind spots, and look for pedestrians, cyclists and other road users. Make sure there is sufficient visibility and space and that the manoeuvre is permitted.

No. U-turns may be prohibited by traffic signs or road rules and should never be attempted where visibility, road layout or traffic conditions make the manoeuvre unsafe.

A road surface warning indicates that the surface ahead may be uneven, damaged or otherwise capable of affecting the safe movement of vehicles.

Depending on the country, it may warn of bumps, depressions, potholes, broken pavement, uneven repairs or other surface irregularities.

Reduce speed where necessary, increase your awareness of the road ahead and be prepared for changes in the vehicle's stability or direction.

Not normally. A warning sign alerts drivers to a hazard rather than establishing a numerical speed limit. A separate speed-limit sign may be used where a particular maximum speed is required.

Where slowing is necessary, it is generally safer to reduce speed before reaching the irregular surface rather than braking sharply while travelling over it.

A severe surface irregularity can affect tyre contact, steering, braking and vehicle stability. It can also damage tyres, wheels or suspension components.

Yes. Two-wheeled vehicles can be particularly sensitive to potholes, ridges and other irregularities because these hazards may disturb their balance or alter their direction suddenly.

No. An uneven-road warning concerns the physical condition or shape of the road surface. A slippery-road warning concerns reduced tyre grip caused by the surface or conditions such as water, ice, mud or other substances.

Yes. A supplementary sign may indicate the distance to the hazard or the length of the affected section, depending on the country's traffic-sign system.

Yes, when conditions require it. Additional distance provides more time to react if the vehicle ahead slows suddenly to avoid a pothole or other surface defect.

Hazardous cargo includes substances and articles classified as dangerous for transport, such as explosives, gases, flammable materials, toxic or infectious substances, radioactive materials and corrosive substances.

Yes, when the applicable dangerous-goods rules require them. Packages and vehicles can require hazard labels, placards, identification numbers or other markings that identify the nature of the danger.

Yes. Dangerous-goods vehicles can be subject to route and tunnel restrictions according to the type and quantity of goods being transported and the classification of the road or tunnel.

A traffic radio service broadcasts information for road users, such as congestion, collisions, roadworks, closures or other conditions that may affect traffic.

It indicates a radio station or frequency on which drivers can receive traffic information relevant to the road or surrounding area.

No. Radio information can help drivers anticipate conditions and choose a route, but drivers must continue to obey traffic signs, signals, road rules and instructions from authorised persons.

A tourist attraction is a place that visitors travel to because of its cultural, historical, natural, recreational or entertainment value.

Examples include monuments, castles, museums, scenic locations, cultural sites, amusement parks and recreational destinations.

Yes. Many countries use tourist or direction signs to guide travellers toward important attractions and places of interest.

A licence plate is a plate displaying the registration identifier assigned to a vehicle. It allows authorities and other authorised systems to identify the vehicle's registration.

Yes. Licence plate, registration plate and number plate are different terms commonly used for the plate displaying a vehicle's official registration number.

Most motor vehicles used on public roads must display one or more registration plates, but requirements differ for motorcycles, trailers, agricultural vehicles and other special vehicle categories.

This depends on the country and vehicle type. Cars commonly require front and rear plates, while motorcycles and certain other vehicles may require only a rear plate.

Yes. A required registration plate must normally remain clearly visible and readable. It should not be hidden by luggage, dirt, accessories or other objects.

Generally no. Changing the characters, colours, dimensions or appearance of an official plate may make it invalid or illegal. Plates and authorised reproductions must comply with local specifications.

Follow the local reporting and replacement procedure. Many countries require the loss or theft to be reported to the police or vehicle-registration authority before a replacement plate can be issued.

A plate must remain legible and compliant with local requirements. If damage prevents it from being read or makes it invalid, it should be replaced according to the local registration procedure.

Some countries allow motorists to request a personalised registration combination. The available characters, formats and prohibited combinations are determined by the registration authority.

This varies between countries. In some systems the plate remains with the vehicle, while in others it remains associated with the registered holder and may be retained or returned when the vehicle is sold.

A charging station is a location where electric vehicles can be connected to an electricity supply to recharge their batteries. A station may contain one or several individual charging points.

Charging stations are intended for vehicles that can be externally charged, such as battery-electric vehicles and plug-in hybrid vehicles. The exact vehicle categories permitted may be indicated by local signs or operator conditions.

Not necessarily. A space beside a charger may be reserved for electric vehicles or vehicles that are charging. Drivers must check the signs and markings before parking there.

Not where the parking space is officially reserved for electric vehicles. An ordinary parking space located near a charger may be different, so the applicable signs and markings determine who may park there.

This depends on the local traffic and parking rules. Many charging spaces require the vehicle to be connected to the charger, even if the vehicle itself is electric.

Charging may be free or subject to payment. The price and payment method are determined by the charging operator, while separate parking charges may also apply.

Yes. Traffic signs, parking regulations or charging conditions may establish a maximum duration to encourage drivers to move their vehicles and make the charger available to others.

Follow the local parking rules and charging conditions. Some locations require vehicles to leave after charging or impose additional fees or time limits when the charging session has ended.

No. A charging station does not allow a driver to ignore no-parking rules, reserved spaces, time limits or other traffic regulations. The vehicle must still be legally parked.

No. Charging stations can provide different charging powers. Some are intended for longer parking periods, while high-power chargers can recharge compatible vehicles much more quickly.

A general danger warning sign indicates that there is a hazard ahead that is not represented by a more specific warning sign in the local traffic-sign system.

It can be used for unusual or uncommon hazards for which no dedicated warning symbol exists. The nature of the danger may be explained by an additional panel, symbol or message.

Look for a supplementary panel, text or symbol accompanying the warning sign. It may describe the hazard or provide information needed to understand the warning.

Increase your attention, observe the road and surroundings carefully and adapt your speed where necessary so that you can respond safely to the hazard.

Not normally. A warning sign alerts road users to danger rather than establishing a numerical speed limit. A separate speed-limit sign may be provided where a specific maximum speed is required.

It is used when the traffic-sign system does not contain a specific symbol that accurately represents the particular hazard.

Yes. A general warning sign may be used for either a temporary or continuing hazard, depending on local signing rules and the circumstances.

Yes. Depending on the country's traffic-sign system, an additional panel may indicate the distance to the hazard, the length of the dangerous section or other useful information.

No. A danger warning sign does not by itself change the priority rules. Drivers must continue to follow traffic lights, priority signs and the normal right-of-way rules.

Not necessarily. The sign normally warns of a hazard ahead of the sign, and the dangerous situation may extend over a section of road. Supplementary information may indicate its location or length.

Rail safety covers the rules, equipment and precautions intended to prevent accidents involving trains, railway infrastructure and people.

Railway crossings bring road users and railway vehicles into the same location. Road users must therefore obey the warning systems and never enter when a train is approaching or the crossing cannot be cleared safely.

Normally, no. Railway tracks are operational transport infrastructure and should be entered only at authorised crossing points or where access is specifically permitted.

A pedestrian is primarily a person travelling on foot. Local traffic laws may also treat people pushing bicycles, wheelchairs, prams or certain other devices as pedestrians.

Pedestrians should normally use pavements, sidewalks, footpaths or other areas provided for pedestrians. Where these are unavailable, local rules determine where pedestrians may walk on or beside the road.

This depends on the country's traffic rules. Many countries require or recommend pedestrians to face approaching traffic, but the exact rule varies.

Use a pedestrian crossing, traffic-light-controlled crossing or other designated crossing where required or reasonably available. Where crossing elsewhere is permitted, choose a location with good visibility and cross carefully.

The exact priority rule varies between countries. Drivers are commonly required to give way to pedestrians using or entering designated crossings, but pedestrians must still obey traffic lights and avoid entering the road dangerously.

Yes. Where pedestrian signals are provided, pedestrians must follow their indications and should not enter the roadway while the signal prohibits crossing.

In many traffic systems, a person who dismounts and walks beside a bicycle is treated as a pedestrian. The precise legal classification depends on local law.

This depends on the road layout and local rules. Pedestrians may sometimes use a cycle path when no suitable pedestrian facility is available, but they must not unnecessarily obstruct cyclists or other authorised users.

Yes. Drivers turning into another road must watch carefully for pedestrians crossing the road they are entering and give way where required by local traffic law.

Check carefully for approaching traffic from all relevant directions, make sure there is sufficient time and distance to cross safely, and continue to observe traffic while crossing.