es decir, el tráfico de carreteras, autopistas, etc. vs el tráfico subterráneo (metros y trenes) ó aéreo.

http://www.roadtraffic-technology.com/contractors/driver_inf...
Traffic Technology is a leading supplier of advanced transportation monitoring technologies, and road safety equipment and services. Through partnership we bring to the UK state-of-the-art technologies for monitoring vehicles, cycles and people, as well as road safety equipment. Our commitment to providing robust customer-driven solutions leads us to work with innovative worldwide manufacturers.

ABOVE-GROUND TRAFFIC MONITORING PRODUCTS
The SDR radar traffic classifier is an advanced radar vehicle detection device capable of monitoring vehicle flow, speed, classification and direction to high degrees of accuracy from a suitable safe roadside location.
Developed through the increased need for safe non-intrusive detection technologies, the SDR provides a direct replacement for in-road tube or loop-based counter classifiers.
With options for remote connection through Bluetooth® and GPRS, the SDR makes the monitoring of vehicles safe, efficient, effective and accurate.

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Note added at 6 mins (2008-09-08 15:57:35 GMT)
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Este "tránsito en superficie" seguramente está contrapuesto a "tránsito subterráneo".