Crash Data for Pittsburgh Highway Corridors

The Southwestern Pennsylvania Commission, I've just discovered, has a great deal of transportation data for our region. Among other things they have a Congestion Management Process which is supposed to collect data on highway congestion so that transportation planners know where it needs to be alleviated.

Of interest to an emergency responder, the SPC posts data on crash location and severity for the regional highway corridors. This I found to be particularly enlightening. For example, here(as a PDF) is the data for I-376 between the Turnpike and Downtown. Some points I thought were interesting:

1. There are noticeably more crashes on Fridays and Saturdays, and I'm wondering why. Instinctively I'd say late night DUI drivers, but that's belied by the next point.
   
   
2. The peak hours for crashes appear to be(in descending order) 14:00, 8:00, 13:00, 15:00, 16:00, and 2:00. Mid-afternoon doesn't seem to me a very accident-prone time, but if these data are correct that obviously needs to be rethought.
   
   
3. 76% of crashes are in non-adverse conditions, which suggests, since Pittsburgh has 152 days annually with rain, snow, sleet, &c., that drivers are less competent or careful when the sun comes out.
   
   
4. 43% of the collisions on 376 were rear-end collisions, and 40% were vehicle into a fixed object(barrier, sign post, and much more).
   

A couple of notes on the data:

The crash data are from PennDOT's CDART crash tracking system. These are "reportable" crashes only, defined by PennDOT and the SPC as "a traffic accident where someone was injured or where one of the vehicles had to be towed from the scene".

The "severity index" they have listed is a weighted average, with the following weights given to each crash type:
Fatal crashes = 12
Major injury crashes = 12
Moderate injury crashes = 3
Minor injury crashes = 2
Unknown injury crashes = 2
Property damage only crashes = 1