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Fourth, there is a particular limitation specific to those alternative work arrangements actions
designed to reduce the absolute number of commute trips involved. The two actions affected are
telecommuting and CWW. The nature of the travel data collection affecting all 82-program sam-
ples was such that numbers of trips eliminated outright by telecommuting one or more days a
week or by reducing the number of workdays by compressing work weeks cannot be ascertained.
Thus outcome analysis based on the 82-program sample can only address effects of associated
mode shifts, exclusive of trip elimination effects. Other available evidence must be drawn upon to
obtain a full picture of telecommuting and CWW effectiveness.
Finally, a reminder as to the role of Chapter 1, "Introduction," is in order. Chapter 1 not only out-
lines development of the Handbook, it also provides important technical guidance in its "Use of the
Handbook" section. One example of the helpful material included is the tabulation, in Appendix B,
of U.S. Consumer Price Index factors for conversions to constant dollars. These may be applied to
give up-to-date context to price and cost data in cited studies from various time periods.
Traveler Response Summary
Examples of effective TDM programs--defined as having a measurable trip reduction--may be
found in all types of environments. Nevertheless, those employers or institutions located near
good transit service have been found to have better-performing programs than those not close to
good public transit. In the mostly exemplary 82-program sample of employers, the sites with high
transit availability had an average program-level vehicle trip reduction (VTR) of 26 percent, com-
pared with 12 percent where transit availability was low.
Employer Support Actions
Employer support actions are by far the most commonly-applied TDM strategies, providing a
necessary--but not alone sufficient--ingredient for TDM program success. They cover providing
better information on travel alternatives to employees, offering assistance in seeking out and using
those alternatives, and marketing and promotional activity to persuade experimentation and use.
Common measures in this group include commuter information services, employee transportation
coordinators, rideshare matching, transportation fairs, on-site transit pass sales, and guaranteed
ride home. One of their important benefits is an increase of employee awareness about TDM-related
alternatives to driving. Employee awareness of individual incentive and assistance programs in
support of alternatives has been found to range from 77 percent down to 15 percent aware.
The average empirically based estimate of site-specific vehicle trip reduction impacts for full-scale
employer support programs alone is on the order of 4 to 5 percent VTR. Such estimates tend to be
drawn from programs that are exemplary more often than not. Employer support programs actually
have the most consistently significant impact where transit accessibility is low, making non-transit
alternatives critical. Support programs are most appropriate and productive when implemented in con-
junction with tangible actions such as provision of transportation services, management of parking
supply and price, financial incentives, or combinations thereof. What is also clear is that simply adding
"more" employee support measures to an existing solid but basic support-only program will have lim-
ited additional trip reduction benefit, but will generally raise the cost of the employer's program effort.
Guaranteed Ride Home
Guaranteed Ride Home (GRH) is a unique form of employer support action. It is effectively a
standby transportation service--insurance that an employee who chooses an alternative to driving
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alone to work has a low- or no-cost recourse when faced with an unanticipated need to get home
at a time when his/her alternative mode is unavailable or inadequate. GRH effectiveness remains
somewhat of an enigma, in that empirical quantitative data on its travel impacts are scarce and not
sufficiently informative. The handful of empirically-based and modeled estimates of GRH impact
ranges from nil to upwards of 5 percent VTR. (The employer support actions average impact esti-
mate provided immediately above is inclusive of GRH effects.) In any case, a good logical argument
can be constructed for the role of GRH as an effective TDM catalyst, and with appropriate limits, it
is relatively inexpensive to provide.
Employer Transportation Services
Employer transportation services include employer assistance with vanpool creation and program
management, transit assistance either in the form of running separate shuttles or contracting with
the transit operator to intensify service, or allowing use of company vehicles for ridesharing or mid-
day business trips. In the 82-program sample of employers, those TDM programs which provided
transportation services were considerably more effective as a group in reducing vehicle trips (22 per-
cent program VTR) than those that did not (14 percent), an 8 percentage point advantage.4
The benefit of transportation services is enhanced in the presence of modal subsidies (monetary
incentives linked to use of the preferred alternative modes) and is damped without modal subsi-
dies. The synergy between transportation services and modal subsidies is both obvious and strong.
Programs in the 82-program sample with services but without modal subsidies averaged slightly
over 9 percent VTR, while programs with both achieved just under 27 percent VTR, almost three
times as much. In a well-studied exceptional case with time-series data available--a Tennessee
Valley Authority program of the 1970s--the VTR for a multimodal transportation services pro-
gram (aided by a gasoline shortage) was 25 percent, increasing to 51 percent with the addition of
modal subsidies, a doubling of effectiveness.
Incentives and Disincentives
Among inducements to use alternative modes, incentives and disincentives encompass a variety
of TDM strategies that constitute "incentives." These may in turn be separated categorically into
non-monetary incentives and monetary incentives. Non-monetary incentives include such strate-
gies as preferential parking, awards, or other special treatment, while monetary incentives are
those that have a tangible dollar value to the employee. Even this distinction still blurs somewhat
in strategies where the financial benefit to the employee is somewhat diffuse, such as prizes and raf-
fles or time off with pay. The most tangible financial incentives are either modal subsidies or travel
allowances, where the association between the incentive and the behavior is visible and direct. Of
course, the incentive must logically be relevant to the travel alternatives available at the site. Many
employers offer their employees a transit subsidy simply because of its tax-exempt advantage,
although in many cases transit is not a viable commute alternative.
In the 82-program sample, those employers who featured transit subsidies in their TDM programs
had an average VTR of 21 percent, versus 14 percent for those who did not. Carpool subsidies, per se,
4 All VTR findings reported from the 82-program sample examination include the effects of not only the TDM
strategy being discussed (with or without employer transportation services in this case), but also all other TDM
actions that may have been in place within the particular programs in question (in this instance, the 34 programs
with employer transportation services on the one hand and the 48 programs without services on the other).
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were not found to be common, but employers who offered them as part of their programs averaged
a 23 percent trip reduction versus 17 percent for those who did not. HOV parking discounts were
a much more prevalent form of subsidizing carpooling, and those programs averaged 26 percent
trip reduction versus 14 percent for those who did not. Travel allowances, which include parking
cash-out, were still an early concept when the 82-program sample data were assembled in 19901993
and are not well represented in the data set. A 1997 review of eight California parking cash-out
programs found an average decline in vehicle trips of 17 percent.
In the realm of "disincentives" to driving, the management of employer parking can play an impor-
tant role. Through controlling parking availability, price, or both, parking management has a major
effect on TDM program success in reducing vehicle travel. The impact is similar in magnitude to
the supportive effect of good transit availability, and the two are most commonly found together.
Those employer TDM programs in the 82-program sample that were accompanied by restricted
parking had average VTRs of 25 percent. If the parking was also priced with parking fees, the aver-
age VTR increased to 28 percent, and if discounts were also offered to carpools or vanpools, the
average VTR was 30 percent.
The combination of parking fees and employer transportation services produces a particularly
strong synergistic effect, with the average of such combinations within the 82-program sample
exhibiting an implied 37 percent VTR. The University of Washington U-PASS program combines
parking pricing, transportation services, and modal subsidies, and has obtained a 31 percent VTR
as measured with time-series data over a span of 16 years. Clearly, if it is more difficult or costly to
drive, TDM alternatives become more attractive.
Alternative Work Arrangements
Alternative work arrangements constitute the final major category of TDM strategies. They include
flexible work hours, staggered work hours, compressed work weeks (CWW), and telecommuting.
An important finding has been that the only work hours strategy with a measurably positive effect
on choice of alternative commute modes is flexible work hours. In many cases use of flexible work
hours has been restricted to employees using alternative modes, which may help explain the syn-
ergy. In the 82-program sample, employer programs that included flexible work hours averaged
a VTR of 20 percent compared to 13 percent for other programs, a difference that may or may not
be wholly attributable to the work hours strategy.
CWW and telecommuting are the only TDM strategies intended to lead to outright elimination of
commute trips by whatever travel mode. CWW programs achieve this with more hours per work
day and correspondingly fewer work days per week or two-week period. A comprehensive 1980s
experiment in Denver involving 9,000 federal employees found the longer work day flattened the
peak, reducing the peak 1/2 hour from 56 to 42 percent of all arrivals; had no adverse effect on
ridesharing or transit use; and reduced vehicle miles of travel (VMT) by a net 15 percent among
participating employees. Employee participation in the program was 65 percent.
Telecommuting has yet to live up to its anticipated theoretical promise as a TDM measure. Surveys
indicate that employees who telecommute from home avoid a physical commute about 1.8 days a
week on average. A Washington State analysis of the special case of telework centers found 83 per-
cent drive-alone mode shares for the daily telework center commute compared to 56 percent for
these telecommuters on days they went to the main work site, detracting from telework center effi-
cacy. A 1998 synthesis-type study of telecommuting overall estimated, starting with empirical
observations, that a regional program would reduce employee VMT by 1 percent or less--and per-
haps not at all--depending on residential relocation decision assumptions. Newer evidence does
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