×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Safety effects of part-time signals?

Safety effects of part-time signals?

Safety effects of part-time signals?

(OP)
On one of our arterials (3 lane, 30 mph, ADT = ~15,000) the detection has failed on a signal serving an office park. We've been getting complants about unnecessary delays due to the sideroad being on recall.

Little traffic comes out of the sideroad after about 6 PM. Several people have suggested putting the signal on flash at night. Has any research been done concerning whether the increased risk of right-angle crashes outweighs the reduction in delay?

This road is due for reconstruction in 2009, so we are loath to make the permittee spend a lot to fix the detection on a signal that may be rebuilt or even replaced by a roundabout in 2 years.

     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

RE: Safety effects of part-time signals?

I would say that the risk of right-angle collisions is more traffic and intersection geometry-related than flash/stop-and-go signal related. (In other words that research would suffer the causation-vs-correlation dilemma.)  If the intersection does not meet a warrant criterion in the off-peak and does not have a history of accidents, especially if it is well-lit, then you'd be fine to put it onto flash mode in the off-peak.

RE: Safety effects of part-time signals?

(OP)
I have found a few references since I posted the question:

NCHRP REPORT 457: Engineering Study Guide for Evaluating Intersection Improvements, p. 13:

Quote:

Benioff et al. (13) define conditions in which flash mode is not likely to cause safety problems. Specifically, they recommend using flashing yellow/red when (1) the total major-road volume is less than 200 vehicles per hour (veh/h), or (2) when the ratio of major-road-to-minor-road volume is greater than 3.0.

and Abdelghany and Connor,  (Guidelines for Operating Traffic Signals during Low-Volume Conditions, p. 30: http://ntl.bts.gov/lib/25000/25100/25167/TNW2006-12.pdf) state:

Quote:

Based on the findings of the different studies presented above, it could be easily concluded that the safety of flashing traffic signals, especially yellow/red flashing mode is questionable. Most of the research showed a statistically significant increase in accidents and especially right-angle accidents, when implementing yellow/red flashing signal. In addition, most of the research tried to identify the relation between different
intersectional characteristics and accident rate when using flashing traffic signals.

They go on to recommend that, after considering sight distance, speed, crash history, etc, red/yellow flash may be used during hours when the volumes would work with TWSC, and red/red flash could be used when AWSC would work.

     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources