Article Contributed on: 11/1/2006 11:50:31 AM
Editor's note: These questions were posed to Kevin A. French, PE, P.T.O.E.
Traffic/Transportation Engineer, Jefferson County after speed wires were placed on Douglas Park Road and Pine Drive to study traffic numbers. The traffic numbers are relevant to a proposed development in the Douglas Park, Pine Drive area that residents oppose.
Mr. French,
Thank you for your return call yesterday re: the results of the traffic surveys on Douglas Park and Pine Road in Evergreen. After further thought on our discussion I have a few more questions.
1. What was the top speed recorded on Pine? on Douglas?
This is difficult to ascertain with our data collection equipment. We do have observations in the 76-9999 category but these are usuallyanomalies in the count data. They occurred on both roadways and at alltimes of the day. The top speeds recorded that would likely be good observations fall into the 36-40 category occurring three times over a three-day period on Douglas and 21 times over the three-day period onPine.
2. What was the average speed of the top 15% speeds for Pine? for Douglas?
Again, this is difficult to ascertain with our data collection equipment and software. On Pine, the 85% speed was 32 mph over a three-day period and the 95% was 35 mph, the number you asked is likely between these two numbers. On Douglas, the 85% speed was 25 and the 85% was 29.
3. Can the machines record times? That would be helpful for telling the police when they should be out ticketing.
The observations are placed in bins of five mph and by hour. The observations placed in the 36-40 category appear to be spread out during the day at both locations.
4. What time of the year were the two tests done before the speed bumps were installed? (To ensure an apples-to apples-comparison)
Douglas Park count completed May 20-21, 1999, 1070 total, Ave 24 mph, 85% 33 mph, 586 over 25 mph. Evidence of inordinate amount of traffic during afternoon peak hours in the northwestbound direction, likely due to congestion at the 73/74 intersection.
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>Douglas Park count completed May 24-25, 1999, 673 total, Average Speed 23 mph, 85% 28 mph, 231 over 25 mph.
5. Were the wires set in the same place on Douglas Park as they werefor the last test? (To ensure an apples to apples comparison)
Actually moved down the road to avoid the speed bumps. Would expect volumes to be the same
6. What was the time period of those original tests? Also 3 days?
Original counts placed for one 24-hour period, per normal Jeffco procedures.
7. Why isn't it a 7-day test for a more accurate representation? Were they counting any weekend days?
Due to staffing constraints, we usually get only one day of counts when evaluating neighborhood traffic conditions. The weekday counts usually only vary by about 10 percent by day of week or month of year on neighborhood roads. We only count weekends if there is a special concern that would only apply on weekends.
8. Is there any consideration given that some people will slow down more than they usually would when they see the markers (unconciously and conciously - not knowing it is a test - thinking maybe it is the police I know I have done this in the past - whether speeding or not, just a gut reaction)
We haven't been able to measure this. I imagine that some people may slow down but normally I don't think many motorists pay enough attention to notice them.
9. Is there a weight limit that registers the speed? I would like to think that me pushing my son's stroller over the wires was not calculated as well.
Vehicles must have enough mass to cause an air pulse measurable by the counters. Strollers and even bicyclists are not likely counted.
10. Would you please clarify for me what you meant when you said, I believe, that 20 mph was very rare and slow for a paved road and it is
difficult to decide what a speed limit should be.
Most residential areas are posted for a 25 mph speed limit. There are only a limited number of roadways in which a 20 mph speed limit is applicable, Douglas Park is likely one of them because of the narrow road section, sharp curve, grade, driveways etc. The speed limit is often determined by the 85 percentspeed and adjusted due to geometric conditions.
11. Also, I believe you said that another traffic study would take place after Labor Day? Will that be in addition to the one that is inplace currently?
Completed on Douglas Park, early-Sept average volume 535 vpd, mid-Sept average volume 480 vpd. The speed numbers were the same Average 21 mph, 85 percent25 mph.
SusanHoffer is a resident of the Douglas Park-PIne Drive area.