Cars per Household
In Figure 11, a pie-diagram is shown of the breakdown of ‘cars per household’ from the Vehicles dataset, weighted by ‘WTHHFIN’. Again, only cars, vans, SUVs and pickup trucks were selected from the dataset (294,409 out of 307,956 vehicles).
From the households that own at least one car, 64% own two or more cars.
Driven distance per vehicle
Individual trip distance
Plotting the distribution of trips over a Cumulative Distribution Function (Figure 13) gives an indication of the percentage of one-way trips that can be covered by electric vehicles with a range equal to the number on the x-axis. However, underlying trip characteristics like driving speed and the use of climate control can significantly affect electricity consumption (paragraph 4). These factors are not recorded in the dataset and the use of the graph is therefore limited.
The graph shows that 95% of trips are shorter than 30 miles, and 99% is below 70 miles. The weighted average trip distance is 9.4 miles. Vehicles owned by urban households averaged 8.5 miles and rural vehicles averaged 12.1 miles.
Overall, trips for errands, meals and school are shortest (See Table 3). Trips for recreation and work are on average the longest, with means of 15.4 and 12.1 miles, respectively. As expected, differences are found between urban and rural households: Car trips to work were found to be (weighted) 3.5 miles longer for rural households (14.8 miles) compared to urban (11.2 miles). Another interesting difference is trips to not so widely distributed services like doctors/dentists, which accounted for 2% of all recorded trips: urban cars used for this purpose travel only 8.9 miles on average, while people from rural households tend to travel almost twice as far (16.7 miles) for these services.
Table 3: Overview of purposes of car trips recorded in the NHTS 2009. Means and 95th percentile distances are given for urban, rural and all trips weighted.
As was mentioned before, significant differences between States can be found for driven distances. It is hypothesized that driving distances are influenced by the:
Studying the impact of these different factors is beyond the scope of this study and perhaps material for further research, but several interesting States can be identified where driven car distances differ significantly from the U.S. mean. One good example is Hawaii, where the State’s biggest island Hawai’i measures 90 miles from tip to tip. The other highly populated islands are O’ahu and Maui, both measure around 45 miles from tip to tip. The longest highway on the Island of Maui is about 60 miles long, looping around the island. From the 1,226 car trips recorded in the NHTS, 99% was shorter than 30 miles and the mean distance was 5.95 miles. Besides the favorable distances in Hawaii for the integration of EV’s, the economics also make sense, as gas prices are the highest found in all of the United States.
The District of Columbia also shows low trip distances, averaging 6.5 miles, as the whole DC area is ‘urban’ and counts only 61 square miles. The only contributor to long car trips would be those that have destinations in neighboring States, for instance commutes to Baltimore, Maryland or perhaps trips to Philadelphia.
Daily driven distance
Cars that were used on their Travel Day in the NHTS made an average of 4.2 trips, yielding a weighted average daily distance of 39.5 miles. The distribution of the total driven distance on the Travel Day is depicted in Figure 14.
With car trips aggregated for the Travel Day, 93% of all vehicle-days show a total distance below 100 miles. It is important to note that only vehicle-days are included where the cars were used that day. As was mentioned before, 39% of cars owned by the participating households were not used on the Travel Day.
Again, a significant difference was found between daily driven distance of urban and rural household owned vehicles. Urban vehicles used on the Travel Day averaged 36.5 miles and rural vehicles averaged 48.6 miles.
As can be seen from Figure 17, approximately 95% of car commuters in the U.S. travel less than 40 miles to work (the weighted average is 13.6 miles). Weighted averages for States vary from 7 miles (Alaska, North & South Dakota) to 22 miles (Mississippi), although the sample sizes of these States (around 200) yields a ~10% error on a 95% confidence interval.
Your comments and any other ideas worth researching are greatly appreciated. Also, please share this with others (this would be a great help to us: simply getting more eyes on our project)