How can I get a quick estimate of traffic volume on my highways without traffic counters or a speed trailer?

Here are 3 quick ways to estimate daily traffic without a traffic counter or speed trailer. Combined with your own knowledge of traffic you can get some pretty good estimates quickly. Note that a full study with a traffic counter is recommended for any detailed study or when determining if you meet a warrant in the Manual on Uniform Traffic Control Devices (MUTCD). Also, if there are seasonal differences a more detailed study may be needed.

Take a 15-minute count during the busiest time of day. Convert that to a daily count using the following formula

Daily traffic = C*F
C = 15-minute count
F = multiplier based upon area:

36 in urban area;
33 in suburban area;
27 in rural area

As an example, if the count is 106 cars in 15 minutes in a suburban area, the daily count would be 3,500 (106*33=3,498).
These approximations only work if there is free flowing traffic (not a traffic jam)

Check if there are bridges in the municipality. Bridges have traffic counts done by the state at least once every two years. Contact your regional office of NYSDOT for any counts. https://www.dot.ny.gov/regional-offices
Use the NYSDOT Data Traffic Viewer to find traffic counts and volumes: http://gis3.dot.ny.gov/html5viewer/?viewer=tdv.
Be sure to check the bridge and short count boxes to see bridges and some counts not on the state system. For instance, Heise Road in the Town of Clarence has a count of 3,486 (from the year 2008) (see figure). While these data are mostly state highways, they can be used to estimate traffic on nearby highways by just doing a rough comparison using your own knowledge.