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Safety Effects of Differential Speed Limits

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APPENDIX B. EXAMPLE OF A CLARIFYING DATA REQUEST LETTER

Appendix B shows an example of a follow up letter providing clarification.

Dear Mr. Wyatt,

Thank you very much for the data you sent to us! Once again we have another question. The accident data we got from you are from 1991 to 2000 as shown below

I77, From Future I-74 to Va. State Line

[The names above refer to counties.]

I have four quick questions:

1. Can we get the ADT by year, from 1991 to 2000, for the accident sites shown above?
2. Do you have any crash data for:
   1. Rear-end crashes involving trucks, and
   2. fatal crashes involving trucks?
3. When tabulating crashes, some States include only crashes on the mainline, and others include ramp crashes as well (regardless of causality). For North Carolina, which should we assume? If it is the case that ramp crashes are included, then do you know roughly how the number of ramp crashes compares to the number of mainline crashes?
4. Is the speed limit for cars and trucks 65 on North Carolina interstates, and has the limit changed since 1990?

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