Traffic calming is a set of street design strategies that slow cars down and reduce cut-through traffic, primarily to make neighborhoods safer and more comfortable for people walking and biking. The tools range from speed humps and narrower lanes to full street closures, and they work by physically changing the road so drivers naturally adjust their behavior without needing police enforcement. On average, traffic calming measures reduce top driving speeds by about 20% and daily traffic volumes by 16%.
The Core Idea Behind Traffic Calming
The Federal Highway Administration and the Institute of Transportation Engineers describe traffic calming as using “self-enforcing physical or psycho-perception means” to get the results a neighborhood wants. In plain terms, that means changing what the road looks like and feels like so drivers slow down on their own. A narrow, curving street lined with trees naturally feels like a place to take it easy. A wide, straight road with clear sightlines feels like a highway. Traffic calming redesigns the first kind of street on purpose.
The primary goals are improving safety for pedestrians and cyclists, reducing noise and pollution on residential streets, and discouraging drivers from using neighborhood roads as shortcuts. These projects show up in urban, suburban, and rural areas, and they target both individual streets and entire street networks.
Vertical Measures: Humps, Tables, and Cushions
The most recognizable traffic calming devices are raised features in the road that force drivers to slow down physically. A standard speed hump is 12 feet long and about 3 inches high. It’s effective: a single hump slows cars to the 15 to 20 mph range. Field studies of 199 speed humps found they reduced the fastest drivers’ speeds by 6 to 13 mph. When installed in a series, they also cut traffic volume by about 20% as some drivers choose alternate routes.
Speed tables are the wider, flatter cousin. They have a 10-foot flat top with 6-foot ramps on each side, totaling 22 feet in length and standing 3 to 3.5 inches high. Because the flat section accommodates a full car’s wheelbase, the ride is smoother, and the resulting speeds are higher: 25 to 35 mph rather than 15 to 20. Speed tables are common where cities want moderate calming without the jolt of a hump.
Speed cushions look similar to humps but have gaps between raised sections, allowing wider vehicles like fire trucks and buses to pass through with their wheels straddling the raised portions. They slow cars to the same 15 to 20 mph range but produce slightly smaller overall speed reductions (5 to 7 mph) in field measurements.
Horizontal Measures: Curves and Narrowing
Instead of bumping cars up and down, horizontal measures force drivers to steer around obstacles. A chicane is a series of alternating curb extensions or planters that create an S-curve on an otherwise straight street. Drivers have to weave back and forth, which makes high speeds uncomfortable. Three field studies found chicanes reduced top speeds by 3 to 9 mph.
Curb extensions (sometimes called bulb-outs) push the sidewalk out into the street at intersections or mid-block, physically narrowing the roadway. They shorten the distance pedestrians need to cross and make walkers more visible to drivers. A related approach, the realigned intersection, introduces curves into what would otherwise be a straight shot through a crossing point, reducing speeds within the intersection by 5 to 13 mph.
Volume Control: Diverters and Closures
Some traffic calming measures aren’t about speed at all. They’re about keeping cars off streets where they don’t belong. These are the tools cities use when a residential street has become a shortcut for commuters.
A diagonal diverter places a barrier across an intersection at an angle, blocking straight-through movement while still allowing turns. This typically cuts daily traffic by 35 to 40%, though reductions can range from 20 to 70% depending on the layout and available alternate routes. A half closure blocks one direction of travel for a short stretch, creating a temporary one-way section that discourages through traffic. Volume drops of 40 to 60% are typical.
A full street closure is the most aggressive option: a physical barrier that blocks all through traffic, turning the street into a dead end for cars while often maintaining access for pedestrians and cyclists. It produces the largest volume reduction of any traffic calming measure. Forced turn islands and median barriers take a more surgical approach, blocking specific turning movements at intersections to prevent drivers from entering or cutting through a neighborhood.
Road Diets: Fewer Lanes, Better Safety
A road diet converts a four-lane undivided road into a three-lane road with one travel lane in each direction and a center left-turn lane. The leftover space often becomes bike lanes, wider sidewalks, or parking. This reconfiguration reduces total crashes by 19 to 47%, a range large enough that the FHWA lists it as a “proven safety countermeasure.”
The safety gains come from several angles. Rear-end and left-turn crashes drop because turning cars have their own dedicated lane instead of stopping in a travel lane. Right-angle crashes decrease because side-street drivers only need to cross three lanes instead of four. Pedestrians benefit from a shorter, simpler crossing. And speeds become more consistent, eliminating the dangerous speed differences between lanes that occur on four-lane roads when one car slows to turn and others swerve around it.
Visual and Psychological Cues
Not all traffic calming involves physical barriers. Some measures work by changing how the road looks to drivers. Street trees planted close to the roadway create a sense of enclosure that makes drivers feel like they’re in a neighborhood, not on an arterial. Narrower painted lanes achieve a similar effect. Textured or colored pavement at crosswalks draws attention and suggests a transition zone. The FHWA groups these under “psycho-perception” features, meaning they influence driver psychology rather than physically preventing speed. These visual cues are often combined with physical measures for a layered effect.
The Emergency Vehicle Trade-Off
One of the most common concerns about traffic calming is whether it slows ambulances and fire trucks. The short answer: yes, but by a measurable and generally modest amount. A standard speed hump costs an ambulance roughly 8 to 10 seconds per hump. Larger ambulances designed for multiple victims lose slightly more, around 10 to 16 seconds depending on the hump. The bigger issue is queue delay. When a vehicle ahead of the ambulance slows for a hump, the ambulance can lose up to 55 seconds waiting behind it, depending on the type of vehicle blocking the way.
This is why speed cushions exist. Their gaps let wide-axle emergency vehicles pass through without slowing as much. Cities also sometimes exempt emergency routes from vertical calming measures entirely, relying on horizontal or volume-based strategies instead.
Impact on Property Values
A study of Portland, Oregon’s traffic calming program found that the average effect on home prices was essentially zero across all projects. But that average hides an important pattern: only the most effective installations, the ones that actually changed traffic conditions noticeably, moved the needle on property values. Projects that reduced traffic by 16% raised home values on the treated street by about 1%. The relationship scales with effectiveness. A separate study found that cutting traffic volumes in half raised prices by 1.4%. The takeaway is that traffic calming boosts property values only when it meaningfully reduces the volume or speed of traffic on your street.