7/31/2012
Reed Hollinshead
ITD Communication
208-334-8881
reed.hollinshead@itd.idaho.gov
Safety, traffic flow improved as speed limit on section of Chinden changed
GARDEN CITY - To improve traffic flow and safety, the speed limit on a four-mile section of Chinden Boulevard (U.S. 20/26) in Garden City will be changed Thursday morning (Aug. 2). This is in accordance with state law giving the Idaho Transportation Department the authority to set limits on all state highways and interstate routes.
ITD met with city leaders from Boise and Garden City earlier this summer, in addition to city police from both areas and Idaho State Police to notify them about the upcoming change.
The speed limit from Eagle Road (Idaho 55) to Coffey Street (on the west side of the ITD District 3 office, across from the U-Haul) will be posted at 50 mph. It was 45 mph for most of that stretch, and 35 mph for the last quarter-mile heading east to Coffey.
The speed limit is being changed to comply with the findings of a summer 2010 study of the speeds motorists drive on that portion of Chinden. ITD traffic engineers set the limit at the speed at which 85 percent of
the traffic is driving to determine a safe and reasonable speed for a
given road section, in accordance with federal safety guidelines. According to research, setting a speed limit according to that 85th percentile produces the fewest crashes.
The posted limit is a maximum speed when there are no obstacles or distractions and the pavement is dry. With icy, snow-covered or slick roads, it is always prudent to travel slower than the allowed limit. The speed-limit guideline is safe and prudent for the conditions.
"Speed-limit signs cannot replace common sense," said ITD's southwest Idaho Traffic Manager, Kevin Sablan. "They are intended to supplement - not substitute for - the driver's judgment."
Limits help determine a reasonable speed for a particular road under ideal weather conditions. Speed Limits are imposed to assist Idaho law enforcement, and enforcement of the limits by them is essential. Limits encourage better traffic flow by reducing the variances in speed from one vehicle to the next, enhancing free-flowing movement.
In determining speed limits, the investigation involves determining the design of the road and its immediate environment. Engineers analyze items such as lane width, pavement type and condition of the road. They also look at terrain, parking conditions, residential development along the road and the number, width and types of entrances and intersecting streets.
Reducing a speed limit does not necessarily result in safer driving conditions. Reducing the limit below the warranted speed can actually be hazardous and unsafe. Studies show that merely reducing a speed limit has little effect on the speed at which motorists will travel. Furthermore, no published research findings have established a direct relationship between lower posted speed limits and crash frequency.