The rise of mobility-on-demand (MoD)

The challenge is to ensure the same benefits of privately-owned cars while removing dependency on non-renewable resources, minimizing pollution, and avoiding the need for additional roads and parking spaces. A lead to a solution for this problem comes from realizing that most of the vehicles used in urban environments are overengineered and underutilized. For example, a typical automobile can attain speeds well over 100 miles per hour, whereas urban driving speeds are typically slow (in the 15to 25-miles per hour range [5, 8]). Furthermore, private automobiles are parked more than 90 percent of the time [5]. Within this context, one of the most promising strategies for future personal urban mobility is the concept of one-way vehicle sharing using small-sized, electric cars (referred to as mobility-on-demand, or MoD), which provides stacks and racks of light electric vehicles at closely spaced intervals throughout a city [1]: when a person wants to go somewhere, she/he simply walks to the nearest rack, swipes a card to pick up a vehicle, drives it to the rack nearest to the selected destination, and drops it off.

MoD systems with electric vehicles directly target the problems of oil dependency (assuming electricity is produced cleanly), pollution, and parking spaces via higher utilization rates. Furthermore, they ensure more flexibility with respect to two-way rental systems, and provide personal, anytime mobility, in contrast to traditional taxi systems or alternative one-way ridesharing concepts such as carpooling, vanpooling, and buses. As such, MoD systems have been advocated as a key step toward sustainable personal urban mobility in the 21st century [1], and the very recent success of Car2Go (a one-way rental company operating over 10,000 two-passenger vehicles in 26 cities worldwide [9]) seems to corroborate this statement (see Figure 19.1, left).

MoD systems, however, present a number of limitations. For example, due to the spatiotemporal nature of urban mobility, trip origins and destinations are unevenly distributed and as a consequence MoD systems inevitably tend to become unbalanced: Vehicles will build up in some parts of a city, and become depleted at others. Additionally, MoD systems do not directly contribute to a reduction of congestion, as the same number of vehicle miles would be traveled (indeed more, considering trips to rebalance the vehicles) with the same origin-destination distribution.

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