ABSTRACT
The United States and Texas in particular have a transportation challenge that requires addressing the following four
issues simultaneously: traffic congestion, environmental pollution, safety and energy dependence. In pursuit of a
solution to these transportation challenges, various technological alternatives have been proposed. Notable among
these alternatives is the concept of dualmode. Dualmode vehicles work like usual roadway vehicles using on-board
energy storage when not on an electrified guideway, but are equipped to be conveyed automatically using electricity
provided in real time from the electric grid when on electrified guideways. This technology can impact both freight
and passenger transportation and adds significant traffic capacity at a fraction of the cost for conventional capacity
additions.Electric power providers have expressed an interest in estimating how much electricity would be needed to
electrically power much of ground transportation. This paper investigates the impact on the existing electric grid of
electrifying highway transportation using a dualmode electric guideway infrastructure paralleling the existing
Interstate highways and urban freeways. Data for the study include electric demand data from the Electric Reliability
Council of Texas (ERCOT) and transportation data in vehicle miles traveled for various personal and freight vehicle
classes from the Texas Transportation Institute (TTI). Transportation energy requirements are converted to gigawatt
hours (GWh) to estimate the capacity and peaking characteristics resulting from the conversion of a large portion of
highway transportation energy demand to the electric grid.

INTRODUCTION
Road transportation today is beset with numerous challenges including traffic congestion, environmental pollution,
safety and energy dependence. Texas has a challenge to grow transportation capacity at a pace adequate to meet the
demand driven by population increases. The Texas population is expected to grow 64% over the next 25 years and
vehicle miles traveled is expected to grow 214%, while road capacity is forecast to grow only 6% over the same
period[1]. This mismatch between the growth in demand and capacity, results in increasing traffic congestion
causing non-productive use of time and fuel while reducing economic competitiveness. Texas also needs to improve
air quality. The major metropolitan areas of Texas are in non-attainment or near non-attainment status regarding air
quality. A major contributor to the air quality problem is mobile emissions due to the internal combustion engine
and a dependence on hydrocarbon primary fuels which are currently the most cost effective energy source for
transportation. A recent Electric Power Research Institute (EPRI) study has shown that even with the current
electricity generation mix, the use of grid-connected vehicles will reduce air emissions[2].
On the safety front, Texas has the second highest number of traffic fatalities among the 50 states with 3,675
deaths in 2003[3]. In 2000 there were 1450 fatalities involving high blood alcohol levels in Texas (38% of all
fatalities) and the Department of Public Safety issued over a half million speeding violations. Clearly driver
behavior is a major factor in both fatalities and accidents causing injuries or property damage.
These combined challenges represent an opportunity for innovation. Solutions which hold the promise of
reduced infrastructure cost, reduced traffic crashes due to driver error and other causes, and reduced mobile
emissions with primary fuel flexibility should be of high interest.
Several concepts such as the introduction of High Occupancy Vehicle (HOV) Lanes, Car Pooling, Electric
Hybrid Vehicles, Fuel Cell technology cars, to mention a few, have been implemented or proposed[4, 5].
Unfortunately, these approaches only focus on the solution of one or two of the key problems. An alternative, which
proposes a simultaneous solution to four of the major problems, congestion, pollution, safety and energy security, is
dualmode vehicles and infrastructure.
A definition of dualmode used in the proceedings of a 1974 Transportation Research Board conference on
dualmode systems, is: [6]
Dualmode transportation is that broad category of systems wherein vehicles may be operated in
both of two modes: (a) manually controlled and self propelled on ordinary streets and roadways
and (b) automatically controlled and externally propelled (or both) or powered on special
guideways. In general dualmode transportation systems can include both common carrier and
private vehicles and provide for the transport of both persons and freight over a common
guideway facility.
Since the dualmode efforts 30 years ago, numerous programs such as the Automated Highway System
(AHS), Partnership for Next Generation Vehicles (PNGV), and FreedomCar have focused mainly on vehicle
technologies and assumed an unchanging infrastructure. This study looks beyond the vehicle boundary and assumes
a new infrastructure. The study investigates the impact, on the existing electric grid, of electrifying highway
transportation using a dualmode electric guideway infrastructure paralleling the existing Interstate highways and
urban freeways.
SYSTEM DESCRIPTION
As a result of the urgent need to improve the transportation system, there have been several studies conducted by
various groups in search of possible dualmode technologies. The system proposed in this study requires the
development of both a new infrastructure and dualmode vehicles that can access the new system as well as
conventional roads. Much like the implementation of the interstate highway system, a dualmode infrastructure will
require a transition over several decades. A brief description of the general idea for the system modeled in this study
is presented in this section. A detailed literature review of dualmode and other major automotive transportation
technology programs are included in a study recently completed for the Texas Department of Transportation
(TXDOT)[7]
Vehicle
This study did not require any assumption on the way dualmode vehicles are powered in off-guideway mode. While
on the guideway, vehicles will be powered in real time, directly from the guideway. This can be done through
inductive coupling, sliding contact, maglev technology or any other suitable means. Because this power can also be
TRB 2008 Annual Meeting CD-ROM Paper revised from original submittal.
Tokan-Lawal, Ehlig-Economides, Longbottom, Akinnikawe, Azcarate 4
used to charge an on-board battery, electric vehicles can leave the guideway with a fully charged battery. The stored
battery energy can be used to power the vehicles while they are off-guideway, for a fully electric vehicle
To optimize infrastructure construction costs, the guideway system will impose size and weight limitations
on the guideway vehicles. The system is intended to accommodate personal, public transit and freight vehicles.
Personal vehicle size and weight constraints should not make consumers reluctant to use the system. On the
contrary, because the system is envisioned to accommodate freight, personal vehicle size and style options much
like what people drive today are envisioned with some light-weighting and aerodynamic improvements. Public
transit vehicles would be personal vehicle (van or taxi) sizes operated in personal rapid transit (PRT) mode to
achieve capacity.
Freight vehicles are assumed to carry light weight high value freight fitting within a 10 ft x 5 ft x 5 ft
envelope with each vehicle capable of carrying two pallets weighing 2200 lbs each. Therefore, the maximum freight
vehicle size will be similar to that of a current sport utility vehicle (SUV). High value goods are conceptually
defined as those goods with a value greater than $715 per ton. Automation on the guideway would enable driverless
operation for freight transport on terminal-to-terminal segments. Driverless operation of freight vehicles will avoid
the current need to aggregate most freight to large loads. Freight that is too large in size or weight to fit within the
guideway constraints would still need to be transported on regular highways or by rail.
Guideway
To avoid intersecting other systems, the electrified guideway should be constructed off-grade, preferably elevated.
An elevated infrastructure could also be used to convey new transmission lines, as well as fiber-optic and
communications cables. Power for the guideway will be supplied directly from the electric grid.
A modular design is envisioned. Guideway automation enables reducing the headway between vehicles to
less than one foot even at high speed, thereby providing a capacity about 8 times that of conventional highways for a
guideway velocity of 60 mph. As such, the elevated construction might be limited to 3 lanes in most applications,
with the extra lane to be used when one lane is shut down for maintenance or in the rare event of a blockage of one
of the guideway lanes.
To minimize vehicle power requirements and to ensure guideway automation, the model in this study
assumes that the guideway on and off ramps provide acceleration and deceleration. Because the guideway operates
at constant velocity, once vehicles are on the guideway, there is no need for any significant braking or acceleration.
Regenerative braking while decelerating or traveling downhill will be captured with some conversion losses.
DATA GATHERING
To investigate the effect of electrifying existing interstate/freeway transportation, as a start, the existing traffic
volume and electric demand data and usage pattern is needed for a given region. A challenge for this study was to
find both traffic and electric data for the same region. Electric data in North America is supplied by electric regions
as shown in Figure 1. Transportation data typically is supplied by state. Figure 1 shows that the Electric Reliability
Council of Texas (ERCOT) covers mainly only the state of Texas. Since, in addition, the Texas Transportation
Institute (TTI) provides detailed information on traffic flow in Texas, Texas was used as the basis for the study. The
regional mismatch due to ERCOT regions missing from Texas and outside Texas was assumed to be only a small
error because these regions involve small populations.
Traffic Data
Traffic data for both the urban case study area (Houston) and the regional case study area (Texas) were obtained
from a myriad of sources including the TTI[8], the Federal Highway Administration (FHWA)[9] and the Bureau of
Transportation Statistics (BTS)[10].
To research the impact of electrifying transportation on the electric grid in the study areas, this study
required calculation of the additional energy demand that will be imposed on the grid by conveying on the new
guideway freight and passenger vehicles currently driven on the freeways and interstate highways.
The calculation required total vehicle miles traveled (VMT) and the hourly volume pattern by each vehicle
class and road type obtained from TTI data[8]. The total trucking freight tonnage for the city of Houston and the
state of Texas obtained from reports compiled by the FHWA[9] were also used. Other required data such as the
average passenger weight[11], average person per vehicle[12] and vehicle payload capacity[13] by class were also
collected from different sources.
To illustrate the sort of data used in the study, Figure 2 depicts a graph of TTI data showing the seasonal
difference in traffic volume by the day of the week. It would be noted that Monday through Thursday is lumped into
a single curve because TTI traffic surveys in the region have not yielded a statistically significant difference in the
TRB 2008 Annual Meeting CD-ROM Paper revised from original submittal.
Tokan-Lawal, Ehlig-Economides, Longbottom, Akinnikawe, Azcarate 5
volume and pattern of traffic for those days. Also notable in the graph is that on average, the peak traffic volume in
Texas occurs on Fridays during the summer months.
Electric Load Data
To ensure a good approximation of the impact of additional electric load on the existing electric grid, the electric
load data used had to overlap the same region for which the traffic study was been carried out. As such, some
historical demand data from the Electric Reliability Council of Texas (ERCOT) was obtained from an internal
database upon request.
The electric load data used for this research was sourced from a 2006 ERCOT energy demand file[14]. This
file contains electric demand data for the year 2006, for the five ERCOT regions (North, North East, South, West
and Houston) in hourly intervals for each day of the year.
Figure 3 is a graph of typical daily electric demand for the Electric Reliability Council of Texas (ERCOT).
The graph displays the average electric demand for each day for 2 weeks, one in January and one in August. It
should be noted that in the ERCOT region, summer is the season with the highest electric demand and August is
usually the month with the peak demand. January on the other hand is on average the coldest winter month in
Texas[15]. This graph is designed to give the reader an insight into the electric demand pattern, based on seasonal
differences, for the study region.