A friend's question:
Are there data about automobile accidents over the course of a year with daily increments and preferably with a large variety of filters like city, highway, etc?
California Polytechnic State University has a downloaded dataset on fatal accidents on the national highway system for the year 2007:
Data.Gov has a number of datasets on accident data by state: https://explore.data.gov/catalog/raw?tags=crash
The NHTSA has summary statistics for 2012 on a state by state basis here: http://www-nrd.nhtsa.dot.gov/departments/nrd-30/ncsa/STSI/USA%20WEB%20REPORT.HTM
The Insurance Institute for Highway Safety has accident/safety ratings per make/model/year, but you will have to scrap it off their site: http://www.iihs.org/iihs/ratings
Some of the city level open data portals also publish traffic accident datasets:
The UK data.gov publishes accident/road safety datasets from 1979 to present here: http://data.gov.uk/dataset/road-accidents-safety-data
I put together an online catalog of sites covering traffic surveys and traffic accidents: http://www.opengeocode.org/opendata/traffic.php
A list of links from albert,
NCSA Publications & Data Requests http://www-nrd.nhtsa.dot.gov/Cats/index.aspx you probably want this guy: http://www-nrd.nhtsa.dot.gov/Cats/listpublications.aspx?Id=F&ShowBy=DocType
super in-depth stats http://www-fars.nhtsa.dot.gov/Main/index.aspx
crash stats archive http://ai.fmcsa.dot.gov/CarrierResearchResults/Archives.asp?p=23
stats and facts http://www.fmcsa.dot.gov/facts-research/art-stats-facts.htm
nhtsa data http://www.nhtsa.gov/NCSA
federal trans safety somtehing http://www.fmcsa.dot.gov/
national highway traffic safety administration http://www.nhtsa.gov/NCSA
more crash stats http://ai.fmcsa.dot.gov/CrashProfile/CrashProfileMainNew.asp
Not sure if my list is better (or worse), because I think it has a lot to do with Andrew's question about national/state levels. If Andrew says it's cool, I'll just have him update his answer with these links:
NCSA Publications & Data Requests
you probably want this guy:
Super in-depth stats
Crash stats archive
Stats and facts
Federal trans safety something
National highway traffic safety administration (NHTSA) http://www.nhtsa.gov/NCSA
More crash stats
Not sure if you need something for the entire nation, but a lot of localities publish versions of this kind of data.
Update (May 2019): Check this new release: https://smoosavi.org/datasets/us_accidents. It contains more than 2.25 million traffic accident records which took place within the US, and will be periodically updated.
The following dataset is recently released and will be periodically updated: https://smoosavi.org/datasets/2019_traffic_weather_events
It covers the entire U.S, and also contains information about other types of traffic events in addition to accidents, such as congestion, construction, etc.
If you want point-level data on crashes (but only for select states), I recommend submitting a data use request to the folks at the Highway Safety Information System (https://www.hsisinfo.org/) . I use that data to do small area research in NC.