You can get a relatively accurate measurement using Google Earth if the road is straight, flat and exposed (image not obstructed by trees or buildings).
Some additional suggestions:
1. Don't use miles as units. Use feet (5280) or meters (1609.344).
2. As previously mentioned, zoom in and find a landmark in the road to measure from - stop lines, pedestrian crossings, etc.
3. You might want to consider adding 0.1% (5.28 feet or 1.61 meters). This is the "short course prevention factor" that is added to all road course measurements.
4. Measure it a few times and take the average.
If there are trees obstructing the view, you could use "Historical Imagery". It's on the drop down menu - "View". This will enable you to view previous images of the area - some without leaves on the trees!