Traffic Counts

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Periodically, the City of Lafayette collects traffic data such as vehicle speed, direction, and volume. This information helps the City in monitoring existing conditions and planning for future changes. These data reports are accessible through either the map or link below.

City of Lafayette Traffic Count Map

This is a dynamic, interactive map providing summary data on commonly requested information such as traffic volume (Average Daily Traffic, both ways) and speed. Click on the points for traffic information about these locations.

Click here to directly access more detailed information in the form of traffic data reports concerning traffic volume, speed, direction, etc.

City of Lafayette Traffic Counts Unmapped

September 2013 Downtown Mt. Diablo Blvd. & Moraga Road Corridor

Common Traffic Count Terms

ADT, or Average Daily Traffic, is the average number of vehicles two-way passing a specific point in a 24-hour period.

85th Percentile Speed is the speed at which 85 percent of the vehicles passing through the study segment are moving at this velocity or slower. Or stated another way, of the vehicles being studied, 15% of the vehicles are traveling faster than the 85th percentile speed. This figure is fairly significant to traffic engineers and transportation planners and is a common measurement of evaluating traffic conditions. By California law, the 85th percentile speed is one of the primary factors used when setting local speed limits.

LOS, or Level of Service, is a common measure used to describe the level of congestion at an intersection. LOS is used to analyze roads and highways by categorizing traffic flow with corresponding safe driving conditions by using a scale that measures the amount of traffic using a given roadway segment or intersection. Levels range from A to F with A representing the highest standard meaning free flow of traffic with no limitations on vehicle movement or speed. Level of Service F usually means vehicles have to wait through one or more signal changes and traffic stoppages of long duration. Lafayette uses two different Level of Service standard methodologies: the Highway Capacity Manual (HCM-LOS) and the Contra Costa Transportation Authority (CCTA-LOS) methodologies. The CCTA-LOS method uses a ratio that compares traffic volumes with the theoretical intersection or road segment capacity. Based on this ratio, a LOS letter grade is assigned. This methodology is useful for planning purposes. The HCM-LOS uses the delay a driver experiences to assign the LOS letter grade. This methodology is more refined and is useful when evaluating the operations of an intersection.