Speed Regulations
Driving Below the Posted Speed Limit

Reducing Speed: When Should You Drive Below the Posted Speed Limit

Updated Oct. 20, 2020

Adhering to a posted speed limit does not guarantee that you are traveling at a safe speed, nor does it always protect you from being cited for “driving at excessive speeds”. The speed limit on any roadway is based on favorable conditions. It refers to a maximum speed at which you can travel when traffic is flowing smoothly, visibility is optimal, your vehicle is functioning properly, and weather conditions are reasonable. Often, driving conditions will not fit this ideal.

If any unfavorable driving conditions increase the likelihood of a crash occurring, or the probable severity of a crash, you must drive at a reduced speed. Usually, it is the sole responsibility of each individual motorist to adjust their speed to an appropriate level below the posted speed limit. Though on certain roadways where conditions are extremely variable, electronic variable speed limit signs may be posted. Even in these cases, it may still be prudent to limit your speed further than indicated on the electronic speed limit sign. You are never totally exempt from the responsibility of choosing a safe speed.

Keep in mind that driving conditions may alter several times over a relatively short distance! Always pay attention to current road and traffic conditions, adjusting your speed to a safe level as necessary.

Heavy traffic

All motorists must reduce their speed below the posted speed limit when driving in heavy traffic. When there are many vehicles on the roadway, the space between vehicles is limited, affording individual drivers less time to react or stop. In extremely congested conditions, attempting to drive at or close to the posted speed limit would almost certainly result in a collision.

Even though it is necessary to drive at a reduced speed during heavy traffic, motorists must also ensure they do not drive too slowly. If the speed you are traveling at impedes the movement of traffic, you may be cited. Drivers who feel more comfortable traveling at lower speeds should always occupy the furthest right-hand lane of the roadway, allowing faster-moving vehicles to pass on the left.

Poor weather conditions

You must reduce your speed in bad weather – and we are not just talking about snowstorms! Even light rain can significantly reduce visibility and your car’s grip on the road’s surface. Obviously, the speed you drive at should be determined by the severity of the bad weather. A 5 mph drop in speed may be sufficient in light rain, while heavy snow would demand a more significant reduction.

Besides rain and snow, other adverse weather conditions which would warrant a reduction in speed include:

Nighttime driving

Some states impose lower speed limits on certain roadways at night. This is usually indicated with a posted speed limit sign. Even where lower speed limits are not established, you must drive at a reduced speed at night. In darkness, your ability to see hazards on the roadway ahead is significantly hindered. Unless otherwise stated, motorists should reduce their speed by 5 to 15 mph when driving in the dark.

Vehicles towing trailers

Motorists should reduce their speed when driving any vehicle towing a trailer, as it will be harder to maintain control. In many states, vehicles towing trailers may only drive in the far right-hand lane of any road with multiple lanes of traffic moving in the same direction. A speed limit of 55 mph or less may also be imposed on such vehicles on highways and other high-speed roads. Check your driving manual for local information on this issue.

School zones & around children

It is essential to reduce your speed when driving in a school zone or any area where children are likely to be nearby. The importance of keeping speed to a minimum around children is reflected in school zone speed limits around the United States. Most states set the maximum speed limit in school zones at 20 to 30 mph, unless otherwise stated on road signs.

In some states, school zone speed limits only apply under certain conditions or at specific times of day. Motorists must ALWAYS keep speed to a minimum around schools, parks, play areas, residential streets and any other area where children may be nearby, even if reduced school zone speed limits do not currently apply.

Blind intersections

An intersection is “blind” if you cannot see at least 100 feet in either direction before entering it and there are no “STOP” signs posted at any entrance. Motorists must drive slower when approaching and entering a blind intersection, as they may not be able to see conflicting traffic approaching from other directions. In California, the speed limit when approaching a blind intersection is set at 15 mph. Similar speeds limits will apply in your state, as detailed in the driving handbook.


The speed limit in alleys ranges from 10 to 20 mph in most states. California traffic law states that drivers must not exceed a speed of 15 mph in any alley, unless posted signs state otherwise. Student drivers should refer to a current edition of the driving manual for information on alley speed limits in their state.

Reduced speed zones on highways

You may encounter special “reduced speed zones” on highways. The lower speed limits on these stretches of road will be indicated with road signs and may be temporary or permanent. In California, motorists will encounter a “REDUCED SPEED AHEAD” warning sign at least 600 feet in advance of the reduced speed zone. Similar warning rules will apply in other states, details of which should be included in the driver handbook.

Reduce your speed gradually and proceed with caution when approaching a reduced speed zone on a highway. Keep in mind that penalties for speeding violations in these areas are often higher, particularly if construction or maintenance work is being carried out.

Reduced speed limit in work zonesWhen going through a designated work area, pay attention to the posted speed limits. Work zones may limit speeds to when workers are present, yet allow traffic to return to the normally posted speed when workers are absent.

Business and residential districts

The prima facie speed limit in residential and business districts varies between 20 and 35 mph around the United States. Most states set the limit in these areas at 25 or 30 mph, with speed limits above 30 mph or below 25 mph being rare. Remember that prima facie speed limits apply when no speed limit signs are posted. When driving in business or residential districts, look out for posted road signs which may indicate a lower speed limit. As always, motorists must reduce their speed further below the legal limit if traffic is heavy or conditions are unfavorable for any other reason.

Animals on the road

Drivers are required to reduce their speed when animals are occupying the roadway or when there is a heightened chance that animals will appear. Whenever you encounter a diamond-shaped animal warning sign by the roadside, slow down and drive with additional caution.

Motorists must reduce their speed significantly when horses, farm animals and animal-drawn vehicles are on the road. When startled by a fast-moving vehicle, horses can cause terrible accidents. If you must pass a horse rider or horse-drawn vehicle, move over to allow the animal as much room as possible. How much you reduce your speed should depend on the width of the roadway and how much space you have. In general, motorists should limit their speed to around 10 to 20 mph when driving around horses.

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