otorists in Platte City at various times have likely noticed a speed trailer sitting alongside a busy roadway, displaying the speed at which passing vehicles are traveling.
Officials say among other things, the purposes of the speed trailer are to encourage drivers to obey the speed limit by making them aware of their speed and to evaluate traffic safety actions and identify traffic pattern changes by comparing data over time for each location where the trailer is deployed.
Joe Wellington, chief for the Platte City Police Department, says the speed trailer deployment program focuses on traffic enforcement efforts to provide more detailed information to elected officials regarding traffic patterns, especially along the city’s three highest traffic routes: Hwy. 92, Fourth Street, and Running Horse Road.
Recently the trailer was placed at the 2700 block of Running Horse Road near the Saint Luke’s Multispecialty Clinic, and the news is mostly good: there was a significant reduction in the number of vehicles that traveled above the excessive speed variation, meaning there are a lot fewer vehicles traveling at a speed 20 mph above the posted speed limit of 35 mph.
The reduction comes when comparing vehicles traveling by during the month of April compared to December. Some of that reduction could be due to the fact that there were more stringent COVID restrictions still in place in December compared to April. Also, various seasonal holiday closings of schools and businesses possibly affected daily December traffic. At any rate, fewer cars on the road per day in December may have tempted some drivers to speed a little more than normal.
Wellington’s report to the board of aldermen says “there was no significant difference in the volume of northbound or southbound traffic for either deployment.”
Later in his written report, details show the average daily number of vehicles in April was 6,643, compared to only a daily average of 5,668 in December, a difference of about 1,000 vehicles per day.
December’s counting period covered 15 days. During that time, 51,8% percent of vehicles were at or below the 35 mph speed limit.
In April, 54.2% of vehicles traveled at or below the speed limit.
In December, there were 159 vehicles (an average of slightly more than 10 per day) traveling past the speed trailer at 20 mph or more above the posted 35 mph limit. In April, that number dropped to just 40, an average of slightly more than three per day.
A speed of up to 10 mph over the posted limit is classified as “acceptable speed deviation” in Wellington’s report. In the December tracking, 99% of vehicles were at or below this number. In April, that percentage traveling with the acceptable deviation was up slightly to 99.1%.
A commonly used traffic analysis standard is speed of traffic at the 85th percentile, Wellington said.
“The speed of traffic at the 85th percentile indicates the speed that most motorists on the road consider safe and reasonable under ideal conditions. It is commonly used to evaluate the appropriate speed limit for any given road segment,” Wellington says.
The 85th percentile speed of traffic on this area of Running Horse during December was 40 mph. In the April study, the 85th percentile dropped to 39 mph, according to the numbers provided by the police chief.
There was only one traffic accident in the study area during the 15-day December evaluation. That was a rear-end collision southbound at Running Horse and Williamsburg Terrace.
Interestingly, the April study period also consisted of only one traffic crash, which also was a rear-end collision at southbound Running Horse and Williamsburg Terrace.
The placement of the speed trailer also helps the police department focus its traffic enforcement efforts by identifying traffic speed patterns. It also helps police determine the amount of speed tolerance that would normally be acceptable when conducting speed enforcement in a specific area.
Based on the latest data, Wellington says his recommendation to elected officials is for the police department to continue to schedule and conduct occasional traffic enforcement focusing on peak hours.
The chief recommends deploying the speed trailer at the Running Horse location again in the fall to evaluate traffic enforcement impact and conduct a comparison on data collected for the year 2021.
“With a deployment taking place again in fall 2021, this will give the department a chance to continue to identify traffic changes during in and out of school periods,” the chief said.