[GIS] Looking for best practices for determining turn penalties

Question

Shortest path routing will often return routes with a lot of turns (zigzag shape).

If you want to get routes with fewer turns, you can use turn penalties to make turning more "expensive".

What are best practices for determining such turn penalties?

The use case:
I would specifically like to get fuel-efficient routes for vehicles. Slowing down, turning and accelerating costs more fuel than driving straight ahead. (Traffic signs – such as stop signs – don't have to be considered.)

Answer 1

Disclaimer: I haven't been up to speed on the research or best practice on this so forgive me if I miss anything and it's been 3 years since I worked with a Travel Demand Model. And when I did travel demand models, I didn't spend a whole lot of time and effort into building turning penalty/restriction models.

Turning restrictions and penalty settings (TR/TP) for the most part are different from intersection to intersection. Usually you can lump sum them into different groups if you're doing macro type analysis.

TR/TP values are usually deployed in the "trip assignment" phase of a modelling process when you know the volumes at each leg of an intersection as well as the intersection geographic layout and green cycle time configuration. Other variables that come into effect are arrival rates, queues, peak hour factors, Average Annual Daily Traffic, Hourly volume data, headways, gaps, etc.. Please check some of the books and publications especially from ITE and TRB. If you are in a university or have access to an academic search engine, metapress has a plethora of articles on turning restrictions and penalties

Some of the issues to consider:

Intersection Type and Configuration

The first issue to look at is signalized vs. non-signalized intersection. In non-signalized intersections, right turns from the major to minor road have a low turning penalty; however, left turning in any direction has a very high turning penalty. Right turns from Minor to Major have a mediocre turning penalty. However, these number change if let's say downstream from the non signalized intersection you have a traffic light. This will generate enough of a natural gap for vehicles to be able to do their turns. On the other hand if let's say you know there is a big generator close by (apartment building or grocery store), then you might have platoons coming up in one direction. For example, vehicle exiting the grocery store onto the major street want to turn left on the minor street. This demand can happen for a very short period during but it could cause massive traffic pattern implications.

In signalized intersections, the main issue becomes the intersection Geometry. The few things to look for are green times including advanced greens, dedicated greens etc, dedicated lanes, and if the dedicated lanes go far enough that in the case of other lanes getting clogged up, does it affect the usage of the dedicated lane. For example an intersection with an advanced green turning left with a dedicated lane will have a low-ish turning penalty value; however, a leg of an intersection that is sharing left/through lanes with no dedicated green turning will have a very high TR/TP. The other thing to look for in signalized intersections is right pocket lanes. At some intersections vehicles will have a dedicated right turning lane. if the lane is long enough and extends far enough then it'll have a low turning penalty otherwise it'll be high.

Calculation method(s)

This is by no means is an exclusive list of methods to calculate TR/TP. Also for the following few days I don't have access to my Highway capacity manual, ITE trip generation manuals, Transportation Planning handbook, and modelling transport book. I have a fewer selection of manuals on me and here is what they have to provide on this issue:

• Travel Estimation Techniques for Urban Planning - NCHRP 365: Note that this document is in the process of getting updated and the new report will be called NCHRP 716:
  • Pages 107-122: describe an older but a basic method to calculate TR/TP
• Turn2000 Turn penalty calculator Documentation
• ArcGIS presentation: The information slide 21 is pretty basic but standard as well
• Simple General Method that could be used as a preliminary analysis
• Trave Model Improvement Program Webinars: Check out the trip assignment videos and lectures for a more detailed overview of the topic.
• Various software: I know that TransCAD, EMME/2 and QRS II do turn penalties different. I don't have access to their manuals but if you can get access to them, check their documentation out.
• FHWA resource on intersection design
• Turning Penalties paper: I haven't read the paper but the abstract looks promising

Note that this is my initial take on the matter. I am missing a lot of technical information that is not included in this answerI will probably update this answer more in 24 hours or so. I hope this helps