Minimizing Energy Use of Mixed-Fleet Public Transit for Fixed-Route Service

Abstract

Affordable public transit services are crucial for communities since they enable residents to access employment, education, and other services. Unfortunately, transit services that provide wide coverage tend to suffer from relatively low utilization, which results in high fuel usage per passenger per mile, leading to high operating costs and environmental impact. Electric vehicles (EVs) can reduce energy costs and environmental impact, but most public transit agencies have to employ them in combination with conventional, internal-combustion engine vehicles due to the high upfront costs of EVs. To make the best use of such a mixed fleet of vehicles, transit agencies need to optimize route assignments and charging schedules, which presents a challenging problem for large transit networks. We introduce a novel problem formulation to minimize fuel and electricity use by assigning vehicles to transit trips and scheduling them for charging, while serving an existing fixed-route transit schedule. We present an integer program for optimal assignment and scheduling, and we propose polynomial-time heuristic and meta-heuristic algorithms for larger networks. We evaluate our algorithms on the public transit service of Chattanooga, TN using operational data collected from transit vehicles. Our results show that the proposed algorithms are scalable and can reduce energy use and, hence, environmental impact and operational costs. For Chattanooga, the proposed algorithms can save $145,635 in energy costs and 576.7 metric tons of CO2 emission annually.

Multi-Objective Vehicle Routing Problem for a Mixed Fleet of Electric and Conventional Vehicles with Time Windows and Recharging Stations

“…According to the SOC of batteries, constraints (12) ensure that the battery SOC at the next node 𝑗 depends on the SOC of node 𝑖 plus battery discharge by traveling from node 𝑖 to node 𝑗. Constraint (13) ensures that the battery is fully charged when exiting the depot.…”

“…Goeke and Schneider [12] used data from Global Positioning System (GPS) to predict energy consumption in simulation environments. Sivagnanam et al [13] utilized real GPS data to predict electricity consumption based on several factors, including vehicle locations, traffic, elevation, and weather data.…”

“…Most studies in GRVP have considered a single objective including traveled distance [5], cost [7,14], emission [9] and fuel consumption [15,16]. Sivagnanam, et al [13] considered an extra objective of emission as a constraint on the solution space. To allow the evaluation of possible trade-offs between multiple objectives, some other works have formulated multi-objective optimization models.…”