Using Vehicular Networks to Collect Common Traffic Data

Hadi Arbabi and Michele C. Weigle {marbabi, mweigle}@cs.odu.edu http://oducs-networking.blogspot.com/

Table 1 shows the ability of DTMon to provide good quality estimation of time mean speed (TMS), travel time, and space mean speed (SMS) compared to current technologies such as fixed point sensors and detectors (e.g., ILDs) and probe vehicle-based systems (e.g., AVL).

Hadi Arbabi and Michele C. Weigle Department of Computer Science, Old Dominion University

ACM VANET, Beijing, China, September 2009

Department of Computer Science, Old Dominion University, Norfolk, VA

Figure 1. Two TOs and four dynamically defined VS in a highway.

Figure 3. Message delay from VS2 with different delivery methods.

High Quality Estimation Conf. ≥ 95%

Traffic Density or

Penetration Rate

Message Delivery Method

Flow Rate and Density High Any

Classification, TMS

Travel Time, or

SMS

Low

SAC, RF+SAC,

or DTR+SAC

Medium or High Any

Figure 2. Message reception rate from VS2 in 5 km segment with 50% penetration rate and medium traffic flow.

Table 2. Required method, traffic density, or penetration rate for high quality estimation of traffic data with 95% confidence (t-test alpha=0.05)

Good Estimate? Sensors and Detectors AVL DTMon

Flow Rate and Density Yes No See Table 2

TMS Yes Underestimate Yes Travel Time Not Available Overestimate Yes

SMS Not Available Underestimate Yes Vehicle Classification Not Accurate Limited Yes

Table 1. Overall comparison of DTMon with other technologies. (t-test alpha=0.05)

Methods of Message Delivery in DTMon   Regular Forwarding (RF) – A vehicle passing a VS will

forward the message (including time, speed, location) to the closest possible TO from the list of TOs defined in the task.

  Dynamic Transmission Range (DTR) – A vehicle will use RF initially with the standard DSRC range of 300 m. If the message cannot be forwarded (i.e., there is no vehicle within 300 m), then the vehicle will increase its transmission range to 600 m. If the vehicle is still not able to find a neighbor, it will increase its transmission range to 1000 m.

  Store-and-Carry (SAC) – A vehicle will store the message and carry it to the next TO.

  RF+SAC – A vehicle will forward the message to the closest TO using RF and will store and carry the message to the next TO in order to ensure reception.

  DTR+SAC - A vehicle will forward the message to the closest TO using DTR and store and carry the message to the next TO.

Quality Estimation of Traffic Data We have evaluated DTMon using ns-3 in free-flow and transient traffic with different market penetration rates. Figure 2 shows the percentage of received messages from vehicles passing VS2 (1 km from TO1 and 3 km from TO5) using different message delivery methods in medium traffic flow rate (1800 vehicles/h). Figure 3 shows the average delay for messages received by the TOs from VS2. RF and DTR have delays in milliseconds. Delay using SAC varies by the travel time of the segment. More forwarding takes place using RF+SAC and DTR+SAC, which results in a lower average delay than SAC.

Table 2 shows the recommended methods of message delivery in DTMon considering conditions such as distance from the TO, traffic density, and market penetration rate.