Traffic Signal Criteria
Difficult deliberations often precede the decision to install a new traffic signal. The Manual on Uniform Traffic Control Devices (MUTCD) lists eight different ways that a traffic signal can be "justified." The eight criteria provide a nationally used, systematic method to evaluate the need for traffic signals. Meeting just one of these eight criteria can be justification for installing signals. However, many other factors need to be considered. Addressing travel needs by alternative means without installing signals may be desirable at some locations even when one or more of the eight signal criteria are met.
To view the criteria for traffic signal installation, refer to the Traffic Signal Criteria document in the right margin of this page.
Traffic will be counted, typically by automatic machine methods that segregate traffic for each approach. Locations that appear close to meeting one or more criteria will receive more intense study, including manual counts that segregate traffic by type (motor vehicle, bicycle, pedestrian) and movement (left turn, right turn, straight through); vehicle delay study; field review of existing intersection conditions; etc.
- When a manual count has been made, on-street bicycle traffic will be included in vehicle volumes before comparing to the criteria.
- Pedestrian volume will generally include those crossing at the intersection and within one-half block of the intersection. The adequacy of alternative pedestrian crossings (safety, travel route, etc.) to meet pedestrian needs will be considered.
- Where "side street" right-turn traffic exceeds 25% of approach volume, all or a portion of right-turn traffic will be deducted before the volumes are compared to the criteria.
- Intersection topography and geometry will be considered.
- The effect and influence of nearby roadway features will be considered. Such features would include driveways, intersections, railroad crossings, etc.
- Future traffic, especially in a growing area, will be considered.
- Traffic redirection resulting from a signal will be considered. This especially includes the impact on neighborhood streets of installing and not installing the signal.
- Benefits to land uses having access to a potential signalized intersection need to be considered.
- The effects of new signals for travel along an arterial highway need to be considered.