CDOT study tests methodology for systematic bicycle traffic measurement

By Robbie Webber

As bicycling and walking have become more popular methods of transportation, cities and states are searching for better techniques for estimating traffic from these non-motorized modes. Both on individual corridors and throughout transportation systems, traffic volumes are essential for planning and performance measures. But measuring non-motorized traffic can be more difficult than counting cars and trucks, so new techniques are needed to estimate traffic patterns.

Colorado DOT worked with researchers at the University of Colorado-Denver to establish Colorado-specific methodologies for estimating bicycle and pedestrian volumes via a limited sample of existing counts. The research surveyed existing practices and findings from other jurisdictions—in both the U.S. and other countries—and then tested counting techniques in several locations in Colorado. Based on the research, the authors made recommendations for best practices for estimating bicycle and pedestrian volumes in Colorado. Although the research was focused on the best methods for estimates in that state, they hope their research will also be useful in other locations.

The research team surveyed methods used for counting bicyclists and pedestrians and suggested improvements that would estimate both commute and recreational trips in different areas of the state. Both on-road and off-road count techniques were examined for pedestrians and bicyclists as well as short-term versus continuous-count methodologies. Variations by season, time of day, and day of the week, and similarities to or differences from seasonal motor vehicle traffic, were also investigated. Finally, spatial variables were analyzed. Land use, age, and socio-economic demographics of the area, and distance to existing on-road facilities or trails were found to affect non-motorized traffic volumes.

By comparing time of day, weekly, and seasonal variations in volumes for both motorized and non-motorized traffic, patterns of recreational vs. commute use became clear. These comparisons also allowed the team to develop factors to estimate annual traffic volumes for different locations. In general, motorized and non-motorized traffic in the same geographic area or corridor did not share the same patterns. Monthly patterns did generally coincide with peaks in the summer months for both modes, but the non-motorized modes showed much greater variation with the seasons. Weekly and hourly patterns were considerably different; and overall, motor vehicle patterns are not good predictors of non-motorized patterns.

Another question explored in the report was, given limited agency resources, whether short-term counters or continuous counters would yield better estimates of overall traffic volumes for bicyclists and pedestrians. Although there are advantages and disadvantages to both types of counters, the researchers concluded that it is more important to collect short-term counts during the times of lowest variability than to install more continuous counters.

Finally, the researchers recognized that different traffic patterns emerged based on whether the count locations were rural or urban, in the mountains or on the plains, and principally used for commuting or non-commute use. Similar patterns were grouped together as “factor groups” and factors were developed to estimate an accurate annualized daily count based on the characteristics of the location and whether continuous counters or short-term counters were being used. The researchers recommend installing five to seven continuous counters for each type of cycling location or factor group. Beyond that, adding short-term counters, which count for a minimum of one week, are more cost-effective than additional continuous counters. They also found that 24-hour counters could be problematic.

Although the methodologies developed for CDOT were specific to Colorado, the research modeling non-motorized traffic volumes from static counts will be very useful for any agency needing to improve their estimates for current and future demand for bicycle and pedestrian facilities.

Robbie Webber is a Senior Associate at SSTI.