  High-definition (Hi-Def) digital maps are an indispensable automated driving
technology that is developing rapidly. There are various commercial or
governmental map products in the market. It is notable that the U.S. Department
of Transportation (USDOT) map tool allows the user to create MAP and Signal
Phase and Timing (SPaT) messages with free access. However, an analysis of the
accuracy of this map tool is currently lacking in the literature. This paper
provides such an analysis. The analysis manually selects 39 feature points
within about 200 meters of the verified point and 55 feature points over longer
distances from the verified point. All feature locations are surveyed using
GNSS and mapped using the USDOT tool. Different error sources are evaluated to
allow assessment of the USDOT map accuracy. In this investigation, The USDOT
map tool is demonstrated to achieve 17 centimeters horizontal accuracy, which
meets the lane-level map requirement. The maximum horizontal map error is less
than 30 centimeters.
