Thursday, February 3

Thursdays: Traffic Engineering Terms

Thursdays of the week is the time to enrich your knowledge in traffic engineering. The following definitions of traffic engineering terms were taken from Dr. Ricardo Sigua in his book Fundamentals of Traffic Engineering published by the University of the Philippines Press in 2008. The terms are quoted below:

Channelization – geometric improvement normally applied at intersections to simplify movements of vehicles to lead drivers to face one conflict at a time.

Clearance interval – the sum of yellow and all-red period in between phases.

Clotoid – a spiral that serves as a transition path as the vehicle enters or leaves a circular curve.

Compound curve – a two-arc simple curve having its centers on the same side of the common tangent.

Cordon counts – counts used to determine the number of vehicles and/or persons entering and leaving an enclosed area.

Crest vertical curve – a vertical curve with the parabolic curve drawn below the two tangents.

Critical gap – describes the minimum gaps needed by drivers of minor road vehicles.

Cycle – one complete indication of green, yellow, and red signals.

D/D/l – a sing-server queuing system with regularity of both arrivals and departures.

Delineators – small reflective panels or buttons mounted on guide posts or guard fences as an effective aid for night driving.”

Other terms will be posted next week. So, wait and learn more.


  1. Hi engineer..
    Remember me??I just want to ask again about the book of Dr. Sigua on the topic about Analysis of Unsignalized Intersection regarding the Basic Capacity of minor road flow graph, what if the Mh(veh/hr)we have gathered exceeds to the given value, 1600 veh/hr, what will we do about it?
    On the other hand, our city is know as "City of Motorcycles", so motorcycles have the highest number in our data collection of traffic count.Is there any consideration for this in the analysis?
    We our having problems in solving and analyzing our data collection.. May you help us..Thank you..

  2. Hi Kramgil,
    **regarding Mh, i'm not certain how you should go about if it exceeds 1600. though you may want to consider checking Dr. Sigua's source of the graph - Organization for Economic Cooperation and Development 1978.
    **are you familiar with PCU values? to obtain the volume in pcu per hour, you need to multiply the volume with the PCU value. as for the case of motorcycles, i think the usual pcu value is about (0.5) to (0.8). so, this will surely answer your problem on its huge number.

  3. We are looking for the source or any related graph but unfortunately..We haven't find one..I also try to search the source of his graph, it wasn't there..
    yah..we have multiplied it to 0.5..
    Thanks for the help Engr..

  4. Good day!
    In connection about your blog, can you define to us the difference between a major road and minor road? In addition to that, our City Planning Office here in Dumaguete City is naming our road in 3 categories; National Road, Major Road and Barangay Road. So if we relate it to Major Minor road of Dr. Sigua's book,in what category would our road falls?
    Thank you for the time.

  5. Hi Kramgil,
    i don't specifically know what road you were referring to. But if you are dealing with an intersection composed of "national" and "major" road then, the major road in your analysis should be the "national" road while your minor road will be the "major" one. Conversely, if you are dealing with an intersection composed of "major" and "barangay" road then, the major road in your analysis should be the "major" road while your minor road will be the "barangay" one. got it?
    don't you have adviser for your thesis? he/she should be guiding you regarding your concerns. nevertheless, i will be a comment away in case you need advise.
    good luck! ;p