# Looking for a term a civil engineer/urban planner might use for a driver:road ratio **URL:** \ **Category:** Factual Questions\ **Created:** [May 4, 2017, 7:09am UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841 "2017-05-04T07:09:09Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![davidmich](https://avatars.discourse-cdn.com/v4/letter/d/e56c9b/32.png) [@davidmich](https://boards.straightdope.com/u/davidmich)\ **Post date:** [May 4, 2017, 7:09am UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/1 "2017-05-04T07:09:09Z")
Hi I’m looking for a term a civil engineer/urban planner might use for a driver:road ratio. Is it driver: road ratio? Countries such as China have policies to restrict traffic on roads by permitting only vehicles with certain license plate numbers on roads on particular days. There must be a term for the ratio of vehicles to roads that would be used (I suspect) in measuring a resulting/anticipated reduction in air pollution. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [May 4, 2017, 3:39pm UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/2 "2017-05-04T15:39:07Z")
I have seen vehicles per mile used for traffic analysis. Dennis ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 4, 2017, 5:05pm UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/3 "2017-05-04T17:05:07Z")
Vehicles per lane-mile is the standard density measure in US traffic engineering. See here for more: [Traffic flow - Wikipedia](https://en.wikipedia.org/wiki/Traffic_flow). The “See also” & “References” section of that article will take you a long way. I have no clue what design method or terms the Chinese prefer. ---
**Author:** ![Crane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crane/32/3495_2.png) [@Crane](https://boards.straightdope.com/u/Crane)\ **Post date:** [May 4, 2017, 5:18pm UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/4 "2017-05-04T17:18:37Z")
LSL. Agreed - also referred to as efficiency of the road surface - road surface covered by projected image of cars on a road segment divided by total surface area of road segment. Crane ---
**Author:** ![Rudiger\_Simpson](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@Rudiger\_Simpson](https://boards.straightdope.com/u/Rudiger_Simpson)\ **Post date:** [May 4, 2017, 5:25pm UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/5 "2017-05-04T17:25:17Z")
If you’re looking for a ratio, there’s the V/C ratio - The volume of vehicles using the road, divided by the capacity of the road. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [May 4, 2017, 5:43pm UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/6 "2017-05-04T17:43:09Z")
How is “capacity” defined in that case? A mile is 5280 feet. If cars are assumed to be 15 feet long you can wedge 352 of them into a mile. But the resulting steel snake will be immovable. ---
**Author:** ![Yllaria](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yllaria/32/3452_2.png) [@Yllaria](https://boards.straightdope.com/u/Yllaria)\ **Post date:** [May 4, 2017, 8:57pm UTC](https://boards.straightdope.com/t/looking-for-a-term-a-civil-engineer-urban-planner-might-use-for-a-driver-road-ratio/785841/7 "2017-05-04T20:57:25Z")
I mostly hear [Level of Service (LOS)](https://en.wikipedia.org/wiki/Level_of_service), which is graded from A to F and sometimes beyond. Because it doesn’t matter how many cars can potentially drive on the road, or even how many are driving on the road. What matters is whether you have to slow down or stop when using it. Sometimes the geometry of the road lowers the LOS. Having interchanges that are too close together can lower a road’s LOS because there are too many cars changing lanes in too short a distance. That’s called a braiding problem. I tried to look up capacity and ended up laughing at the first doc that came up. I think they meant “maximum hourly rate”. > [@](#): > > The Highway Capacity Manual(2010) defines the capacity as the maximum howdy rate at which persons or vehicles can be reasonably expected to traverse a point or a uniform segment of a lane or roadway during a given time period, under prevailing roadway, traffic and control conditions. Some days my howdy rate is near zero. There are rules of thumb for estimating a road’s capacity. But if you want to know the actual capacity, you need to go out and count cars until you find the break point between LOS A and LOS B. Or between whichever LOS you’re willing to put up with and the next lower.