OLR Research Report

September 22, 2006




By: James J. Fazzalaro, Principal Analyst

You asked what the difference is between a speed bump and a speed hump. You also wanted to know where they can be installed—only on local roads or on state roads as well and who is responsible for damage sustained by a vehicle when going over one.


Speed bumps and speed humps are among many types of “traffic calming” measures. Speed bumps are applications, usually asphalt, that are from two to six inches high and one to three feet from front to back. Speed humps are usually less than four inches high but 10 to 12 feet from front to back. A third version of this type of traffic calming measure is known as a speed table, which is about the same height as a speed hump but considerably longer to accommodate a long flat surface and sloping ramps from street level to the table. A typical length for a speed table would be about 22 feet from front to back.

These types of traffic calming measures are designed for relatively low speed roads. The maximum comfortable speed for crossing a speed bump is about five miles per hour so they are usually only appropriate for parking lots, private roads, and some low speed residential streets. Speed humps typically are used on residential streets where speed limits do not exceed 25 miles per hour. Speed tables are appropriate for roads with slightly higher travel speeds.

The relatively low speed requirements for speed bumps, humps, and tables generally make them more appropriate for municipal streets than state roads, although use at both levels is theoretically possible. In practice, they are likely to be found more commonly on local residential streets. Several Connecticut municipalities have made use of speed humps and Hartford has used speed tables in some areas.

Generally speaking, if a municipality encounters liability problems for damage vehicles may sustain after going over one of these traffic calming measures, it is more likely to be related to things like whether motorists were properly warned of their presence, and whether the measures were properly constructed according to specifications and adequately maintained than the decision to employ them itself.

There appears to have been at least two unpublished Connecticut court decisions that ruled against the use of speed bumps by private property owner associations based on the argument that they adversely affected emergency vehicle response times to the extent that it constituted a public nuisance. The decisions were summarized in the May 1980 issue of the ITE Journal, but they do not appear to be otherwise available. The decisions may have limited applicability to your question in that they involve (1) use of these devices by private property owners and not public authorities and (2) only the use of speed bumps and not speed humps or speed tables.


Speed bumps, speed humps, and speed tables are all related, differing mainly in the length of the raised portion of the impediment. A speed bump is generally designed as a rounded, raised pavement structure usually from two to six inches high. It usually is designed to be from one to three feet “long” (from the front of the bump to the back). A speed bump may be as little as a foot “wide” (from one side to the other) or as much as 10 feet wide, depending on the intent of the measure and the nature of the road to which it is being applied. Their design generally dictates comfortable crossing speeds of five miles per hour or less so they are usually appropriate only for use where vehicle speeds are typically the lowest to begin with such as parking lots, private roads, and on some residential streets.

Speed humps are essentially derived from speed bumps to serve a slightly different purpose. They are typically designed not to exceed four inches high and are usually from 10 to 12 feet long. The purpose of the length of a speed hump is to allow the entire vehicle to be on the hump at once before it descends the far side onto the pavement. This is to reduce the likelihood that a vehicle will “bottom out” when going over the speed hump. When lesser distances are employed, the speed hump behaves more like a speed bump. Speed humps are typically applied to residential streets where speed limits do not exceed 25 miles per hour.

Vehicle behavior and the forces felt by vehicle occupants are different for each, which is why they have different applications. With speed humps, as vehicle speeds increase, the vertical forces on the vehicle increase and occupant discomfort increases as a result. The opposite happens with speed bumps. The peak vertical acceleration, and thus the occupant discomfort associated with this, are greatest at relatively low speeds and decrease as the speed at which the vehicle encounters the bump increases. This is because the vehicle's suspension tends to absorb the vertical forces before the vehicle body has time to react. This is why bumps are used where traffic is already going at a relatively slow speed.

Speed humps are generally used for three purposes: (1) increasing the safety of residential streets, (2) improving the environmental quality of residential neighborhoods, and (3) improving traffic flow throughout a residential area.

Speed tables are the next level application. They are essentially derived from speed humps. They are about the same height (three to four inches) but longer than speed humps. They usually have a long flat top and ramps that may be more gently sloped than speed humps. This gives them the ability to handle vehicles at higher speeds. Typically, a speed table might be 22 feet long with a 10-foot top and six-foot ramps on either end. This design allows their use in situations of 85th percentile speeds of up to 30 miles per hour. (In traffic engineering, the 85th percentile speed is the speed at which or below 85% of the vehicle stream is traveling). Speed tables sometimes have a top surface constructed with brick or some other textured material that makes them more noticeable and serves an aesthetic function.


Traffic calming measures, including speed bumps and speed humps, can be implemented whenever the authority with jurisdiction over the road or street believes that they are necessary and appropriate to the situation. This can be on roads under municipal jurisdiction, where, in fact, some Connecticut municipalities have already used them, or on state roads. However, as explained above, the function and design of speed bumps and speed humps makes them more appropriate for relatively low speed roads than for roads with higher speed limits. Since the majority of state highways typically carry traffic moving at speeds over 30 miles per hour, they are not usually considered appropriate for state highways. But municipalities have many more residential style streets for which they may be useful as way of further calming traffic. In Connecticut, Mansfield, Norwalk, and Stamford have all made extensive use of speed humps and Hartford has used speed tables.


Governmental Liability

The extent to which a municipal or other governmental authority that installs a traffic calming measure, including those discussed above, might be liable for damage a vehicle sustains while encountering the measure appears to be governed by general principles of tort liability as they relate to government actions. The discussion that follows is based largely on an analysis of these issues found in an extensive report on traffic calming practices published jointly by the Federal Highway Administration and the Institute of Transportation Engineers (ITE) in 1999. The ITE is a nationally recognized education and scientific association of transportation engineers and other professionals that conducts research, establishes guidelines and standards, and performs other activities aimed at applying technology and scientific principles to all aspects of transportation.

According to the report, when government's duty to exercise ordinary care for motorists' safety, who are themselves exercising ordinary care, is breached and injury results, a tort claim for government negligence may follow. To establish this liability, several things must be proven including: that there was a breach of duty through failure to perform or negligent performance of the duty, that the breach was a proximate cause of the accident, and that damages resulted.

Governmental functions that are discretionary as generally immune from tort claims under sovereign immunity, but functions that are ministerial generally are not. Discretionary functions are those that involve a choice among valid alternatives. Ministerial functions involve operational decisions that leave minimal leeway for personal judgment (Traffic Calming: State of the Practice; FHWA-RD-99-135, August 1999, p.132). The report gives as examples of discretionary functions the decision to spend public funds on traffic calming, to install one set of measures versus another, and to design a measure for one speed versus another. Examples of ministerial functions include the duty to warn motorists of traffic calming measures that require slowing down, maintain measures in safe condition, and construct measures according to design specifications.

The report notes that courts tend not to second guess discretionary decisions by public officials if there is a reasonable basis for them. The implication of this analysis appears to be that the more likely ways in which a municipality might be found liable for vehicle damage from use traffic calming measures would be if it did not adequately warn drivers of their presence and use, did not maintain them in a safe condition, or did not construct them to accepted specifications.

Exceptions in Connecticut to Immunity for Discretionary Acts

There are three exceptions or circumstances under which liability may attach even though a municipal employee's act was discretionary: (1) where the circumstances make it apparent to the public officer that a failure to act would be likely to subject an identifiable person to imminent harm; (2) where a statute specifically provides for a cause of action against a municipality or municipal official for failure to enforce certain laws; and (3) where the alleged acts involve malice, wantonness or intent to injure, rather than negligence (Colon v. City of New Haven, supra, 60 Conn. App. 178, 180-81; Evon v. Andrews, 211 Conn. 505).

For the “identifiable person/imminent harm” exception to apply, the injured person must allege facts sufficient to support a finding both that he is an identifiable person and that he was subject to imminent harm. (Shore v. Stonington, supra, 187 Conn. 156). The term “identifiable person” applies not only to identifiable individuals but also to narrowly defined identified classes of foreseeable victims (Burns v. Board of Education, 228 Conn. 640, 646 (1994)).

In grappling with this difficult issue, the state Supreme Court has held that the class of possible victims of an unspecified fire that may occur at some unspecified time in the future is not a group of identifiable people (Evon v. Andrews, 211 Conn. 507, 508). It also held that a person killed by an intoxicated driver 50 minutes after the driver was stopped and warned by a police officer was not an identifiable victim (Shore v. Stonington, 187 Conn. 156 (1982)).

Under the “imminent harm” aspect of this exception, any dangerous condition must be more than something that could have occurred at any future time or not at all and must not depend on a “wide range of factors”

before the harm occurs. (Evon v. Andrews, 211 Conn. 508). The prospect of harm must be significant, foreseeable, and limited in duration and geographical area (Pruzycki v. Fairfield, 224 Conn. 101, (1998)).

Other Exceptions Related to Use of Speed Bumps in Certain Circumstances

There have been some instances where courts appear to have created a distinction in the protection afforded to governmental discretion in the choice of traffic calming measures with respect to the choice to use a speed bump (as distinguished from a speed hump). In Mississippi for example, the Mississippi Supreme Court found speed bumps to constitute an inherent danger to motorists. In cases relevant to Connecticut, there appears to have been at least two unpublished court decisions relating to speed bumps. However, their relevance to the issue of municipal authority to use this type of traffic calming measure seems somewhat limited in that the cases involved use of speed bumps by private property owners' associations rather than public authorities.

In the ITE Journal for May 1980, Allan Davis reported that a January 1980 judgment of the Stamford Superior Court had ruled against the use of speed bumps by a private association some of whose members sued over their installation. (It appears the case may have arisen in Darien.) The court apparently ruled their use to be a nuisance based on testimony that emergency vehicles could be delayed up to three minutes in their response time and that the delay can cause serious injury, loss of life, or increased property damage. The court also ruled that the use of the speed bumps obstructed the plaintiffs' right-of-way in derogation of their property rights.

The article also mentions that the court cited a previous case in Greenwich where a court found that speed bumps (again used on certain private roads) constituted an absolute public nuisance, again, largely based the fire and police chiefs testimony that there would be a delay in response time and the testimony of emergency medical personnel that patients could be in danger of suffering additional injury if treatment was continued while navigating the speed bumps. (ITE Journal, May 1980, “Speed Bumps Enjoined in Connecticut”, p. 16).

We attempted to get these decisions, but they appear to have been unpublished. The extent to which they may provide a precedent with respect to the use of speed bumps by municipal authorities appears somewhat limited in that in neither case did it appear that the speed

bumps were put in place by the town's legal traffic authority. We would also note that the cases involved the use of speed bumps and not speed humps or speed tables.