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


Factors not readily apparent to driver in ETS

Factors not readily apparent to driver in ETS

Factors not readily apparent to driver in ETS


Is there a textbook source I can research to understand factors considered "not readily apparent" to a driver in an Engineering and Traffic Survey that cities use to set speed limits?

I would also appreciate if you could tell me your opinion on the possible "not readily apparent" factors I list below, in particular A and B.

I want to provide arguments to invalidate a survey in court. The survey states the 85th percentile for a street is 40.7 mph, which sets the presumptive limit to 40 mph. The engineer is required to state a justification why the posted limit is 35 mph. In the survey the engineer does not articulate reasons in details, but merely lists 4 keywords as follows. Are these 4 factors considered "not readily apparent" by all traffic engineers? Especially I am wondering about A and B since C and D should be wrong.

A. On street parking. I want to argue that parked cars are readily apparent to the driver. In fact the nearby road has on-street parking and has a 40 mph posted limit.

B. Bus route. Similarly, it seems to me that buses are larger-than-cars vehicles which are readily apparent to the driver. In fact, the nearby road has a bus route and a 40 mph posted limit. There is a bus every 30 min weekdays.

C. Midblock crosswalks. There are no midblock crosswalks, so the engineer is wrong on this point.

D. Horizontal curve. The road is straight except the last part after an intersection has a curve, which should really be part of the next speed zone. Regardless, CA code 22358.5 states that road curvatures are readily apparent to the driver, so the engineer appears to be wrong on this point.

Thank you all for taking the time to read!

By the way, the road has 2-lanes each way.

RE: Factors not readily apparent to driver in ETS

It sounds like the engineer that wrote the survey should have been more explicit, but that doesn't mean he's wrong.

On-street parking: How wide are the travel lanes and parking lanes? Is there room for a driver or left side passenger to open a door without causing a collision with a passing vehicle?

Bus route: Buses are obvious (or should be, anyway). Some of the effects they cause may not be. If the street doesn't have bus pull-outs, a shock wave will propagate upstream when the bus stops for a passenger. If the traffic is near capacity, the shock wave can go quite a ways before dissipating.

Mid-block crosswalks: The engineer may have been referring to people crossing mid-block. Long blocks, mid-block bus stops and on-street parking will often lead to mid-block crossings.

Could you give us a Google maps or Bing maps link to the site? If we could see the context, maybe we could be helpful. I'd look for crash history, pedestrian traffic generators in the corridor, zoning and other environmental conditions, and so forth.

To me, it sounds like that law may be outdated. A good traffic engineer would look at the relationship between the street and it's environment and consider what the 85% speed should be, not what it is. Remember that crash severity increases with kinetic energy, not speed. A pedestrian struck by a 40 mph car is probably going to die.

RE: Factors not readily apparent to driver in ETS

Thank you so much for offering to help! As a physicist, I shall defend all engineers from physicists :)

The speed zone is in the link below, Temple City blvd between Las Tunas dr (north intersection), and just past the Lower Azusa intersection (south up to the railway).


On-street parking: I don't imagine the Google Map measuring tool is super accurate, but the total width of all 4 driving lanes and parking lane(s) seems to be about 55-57 ft. I live there and there are usually very few cars parked on the street (residents park in their garages), and you can drive both lanes in each direction even with cars parked. I believe that you still have to be careful when opening the door but it's a low-traffic road except for rush hour (and even then it's never grid-locked).

Bus route: There are no bus pull-outs, however, the traffic is usually pretty light.

Mid-block crosswalks: The housing is all single-family and residents park in their garages. Therefore, I believe all visitors park directly in front of the house they are visiting, I've never seen anyone crossing mid-block. I also went up and down the road with Street View and all bus stops were right by an intersection. Therefore, the bus stops should not cause mid-block crossings.

From the 2010 traffic survey, the accident rate was 1.78, and the expected accident rate was 3.55. The accident rate is not cited in the "not readily apparent" factors. I and my wife are residents, people routinely drive 50+ mph on that road. The city should perhaps try traffic calming devices first, instead of handing out $500 tickets (California), consistently with the intent of the speed trap legislation.

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! Already a Member? Login


eBook - Manufacturing the Cars of Tomorrow
In this ebook, we'll explore how additive manufacturing is going to transform the way cars are made. This includes commentary from thought leaders such as Ford's CTO, Ken Washington, Customer case studies of ways 3D printing is being used today, and a variety of part examples where 3D printing is already impacting how automobiles are made. Download Now
White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. Download Now
White Paper - Analysis and Simulation in Aircraft Structure Certification
Organizations using simulation and analysis tools effectively see the benefits in their ability to achieve certification faster and with drastically less total cost than those who do not maximize these tools. Read this White Paper to learn about how digital tools such as analysis and simulation help in aircraft structure certification. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close