Last week I posted about all of the great information you should get from online aerials. So why do you need to go out in the field when everything is right there on the aerial? First, because the aerials aren’t always right.
I worked on a church project in a fast growing suburb. We got out in the field and realized one of our study intersections didn’t exist and there were two new intersections we had to account for in our study. The roads in the study area were rebuilt during the summer and the aerials weren’t up to date. We had to adjust our data collection to account for reality. Imagine if we turned in a whole traffic study based on the obsolete road network? Our study would have had zero credibility.
Field Review of Physical Features
The second reason to go out to the site is that there are a lot of important details you can’t always see on an aerial. In addition to verifying the information on your hand sketches is correct, add the following details to them while you are in the field:
- Transit Stops
- Traffic Signal Operations (Protected Left Turn Phasing is shown on the left, Protected/ Permitted Left Turn Phasing).
- No Turn on Red Restrictions
- Parking Restrictions
- Speed Limits
- Any road construction in the area that would affect your “normal” traffic counts?
- Any construction or signs for developments near your site?
- Excessive grades or slopes that make widening a road/ intersection difficult?
- Any objects on corners of intersections that block a clear view of oncoming traffic or pedestrians?
While you are at the site, take plenty of pictures. Get one photo of each approach to each study intersection (my iPhone has become a very useful all in one field tool with it's maps, camera, stopwatch, etc). Make sure you keep a log of the photos so you can identify them back in the office. Taking pictures has saved me more than one field visit. It’s amazing how often one little detail is usually missed while you’re doing your field check.
An intriguing alternative to taking pictures is taking your own video log. I haven’t purchased a video system yet, but I am considering the Dual Car Camera Voyager Pro w/ GPS Tracking Logger. It’s a camera, logger you mount on your windshield. You download the recorded file from a removable SD Memory Card. The software interface shows your video next to a GoogleTM map that is tracking the corresponding car location.
Field Review of Traffic Operations
In addition to documenting the existing conditions of the environment, you should observe how traffic operates in your study area during rush hour. I like to go through my hand sketches after lunch and then drive around the road network during the evening rush hour. Things I’m looking for:
- Do shoulders get used by cars as separate right turn lanes?
- Do the traffic signals along a corridor seem to be coordinated so through traffic moves down the corridor smoothly?
- I take a stop watch along and do a few spot checks of each traffic signal cycle.
- Are there any queues that back up out of turn lanes into the through lane or do queues extend back from one intersection blocking the upstream intersection?
- Is it hard to turn onto a major street from a cross street that has a stop sign?
- Think about the routes cars will take to get to/leave your site.
These firsthand observations will save you in a public hearing. I’ve been put on the spot about citizen’s observations of how bad traffic is. If I’ve been out there during rush hour, I can come back with “I went out during rush hour and I saw that, here’s how I incorporated that into my recommendations…. (or I didn’t see that, how often does that happen?).”
And of course, the field visit is part of your quality control process to ensure the details in your traffic study are correct. The quality control process in my office is: (1) the technician draws the sketch based on the aerials, (2) she verifies/corrects the information during a field visit (she also figures out if we need to change the data collection plan as well as determines good parking spots for our data collectors), and (3) I go back to verify her drawings (usually she has created the existing conditions diagram we’ll use in our traffic study report by this point) while I am out to observe rush hour traffic operations.