The Office of Transportation collects 24-hour counts of vehicles and vehicle speeds information on a variety of Portland streets. From this data we can do studies of traffic trends for specific projects such as new construction or to analyze speeding trends for traffic calming. Businesses can also look at just how many people drive or bike by their shop or building. For more information contact: email Tom Jensen or call 503-823-5211.
How We Gather the Counts
We typically use automatic traffic counters to collect traffic data. These counters are usually a metal box with a basic processor, some memory and air switches located by the side of the roadway. They are used to record these types of vehicle information:
- Volume: This is the most common type of traffic count which records all air pulses and divides by two to determine the number of vehicles. In areas with a lot of multi-axle trucks the number recorded by the traffic counter can be larger than the actual number of vehicles. Volume counts are typically 24 or 48 hour in length.
- Velocity: The counter is set up with two equal length hoses to record vehicle speed. It does this by timing the vehicle across a known distance between the two hoses, typically 2’. They classify each vehicle by number of axles so the total volume may be closer to the actual number of vehicles crossing the hoses at the study site. Velocity counts can only be done over one lane of traffic. Vehicles traveling too slowly (<5mph) or too closely together may not be properly counted. These counts last at least 24 hours.
- Classification: These are the least common counts. The counter is set up to attempt to classify each vehicle according the number and configuration of axles. Most of the caveats that apply to velocity counts apply here as well.
- Bike Only: This count type is fairly new and is only available on certain streets. It collects simple bike counts by direction.