Abstract:

Geometric configurations of highways such as cross-sectional
elements affect traffic characteristics such as flow, density, and speed of
vehicles. This review paper is an attempt to understand the effects of lane
width on speed of vehicles. Several papers are mentioned and they illustrates that
lane width of highways affect the operational characteristics of highways such
as speed, capacity, etc.

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1.     Introduction

The lane width of a roadway affects the comfort of driving,
operational characteristics, Level of Service (LOS) and in some circumstances,
the likelihood of crashes. Cross-sectional elements of highways consist
of: travel lanes, shoulders, cross slope,
barriers, curbs, gutters, sidewalks, and medians. A travel lane should have suitable width that is
able provide traffic demand. Table 1 provides the values for
the width of traveled lanes that
are related to the traffic volume and design speed of the two lane
highway.

Table
1: Width of traveled way of a two lane highway (AASHTO Green
Book, 2011)

Preferable range of travel lane width according to the lane type is
shown in Table 2. The width of travel lane for arterial roads is 3.6 m. However,
lanes of 3.6 m cost more than 3.3 or 3m for construction, they cost less
regarding maintenance. Due to wideness of the travel lanes on arterial roads, wheel
concentrations at the edge of pavement are reduced; thus maintenance cost for shoulders and pavement surface is reduced. In places where unequal lane
widths  are used, locating the wider lane
on the outside lane provides more space for large vehicles that usually occupy
that  lane, provides more space for
bicycles, and allows drivers to keep their vehicles at a greater distance from
the right edge.

Table
2: Recommended width of travel lane (AASHTO Green Book, 2011)

Width of
travel lane (m)

Recommendations

2.7 – 3.6

Width of travel lane

3.6

High speed & high volume highway

3

Low speed facilities

2.7

Used occasionally in urban areas if:
• Traffic volume is low, and
• There are extreme right-of-way constrains

3

Auxiliary lanes (like left, right,
and U turn lanes)

3 – 4.8

Two Way Left Turn Lanes (TWLTLs)

2.
Aim
of the Study

The aim of this study is to know the effects of lane width on
speed. The study focuses on vehicle speeds at different types of highways, and
land use. The types of lanes of the highways in urban and rural areas are also
taken into consideration in the study.

3.
Literature
Review

Many studies have been done about the effects of lane width on
speed of vehicles. Rosey, et al. in 2009 studied the impacts of narrower width
of lanes on speed. Fixed-base simulator and real data were compared for knowing
the impacts of lane reduction on speeds. The
study was conducted in two steps: first, 43 drivers drove the simulators on two
configurations of lane widths (3 and 3.5 m); second, the results of the
simulator were compared with a field study, which was conducted by French field
study carried out on a rural road. The results of the study showed that reducing
the lane width did not have impacts on vehicle speeds, but did induce the
participants to drive closer to the center of the road. It also showed that
oncoming vehicles induced subjects to move toward the right side of their lanes.

Ibrahim, et al. in 2017 evaluated the effects of lane width and
roadside alignments on speed, lateral position, and possibility of comfortable
overtaking in exclusive motorcycle lane. Field experiment was conducted along a
predetermined stretch of an exclusive motorcycle lane along the Federal
Highway, Route 2 in the state of Selangor, Malaysia. The stretch over which the
experiment was conducted had a total length 20 km comprising both northbound
and southbound with an average riding time of 20 min.  The length of the roadway was selected in
accordance to the roadway characteristics, availability of a long tangent
section to detect overtaking events, and availability of suitable drop-off and
pickup points. Along the selected route, average lane width was 3.05 m.
Off-the-shelf DR- 9100 unit manufactured by Horiba Ltd was used as a data logger
to record real-time riding speed, video output, electrical signals and outputs
from acceleration sensor simultaneously. Two cameras of high resolution were
fixed on the center front and at the back of the motorcycle to provide
real-time video images of the forward view and the area directly behind the
motorcycle. In an overtaking event, participants’ lateral position and
proximity to the front motorcycle was estimated using ultrasonic distance
sensor. Participants were 29 motorcyclists with average age of 25.6 years old.
Descriptive statistics of overtaking events on tangents and curved sections of
lane is shown in Table 3.

Table 3: Descriptive statistics of all overtaking events (Ibrahim,
et al., 2017)

Overtaking
events N=413

overtaking
speed (km/h)

Lane
with (m)

Maximum
lateral acceleration (g)

Average

Std.Deviation

Average

Std.Deviation

Average

Std.Deviation

Tangential
sections N =367

75.97

8.35

3.05

0.16

0.41

0.15

Curved
sections N =46

64.26

13.34

3.03

0.22

0.32

0.09

The overtaking speed on tangential sections of the roadway is
higher than the overtaking speed on curved sections. A motorcyclist on curved
sections needs a greater distance and acceleration to reach overtaking speed on
straight sections. The researchers used several variables in the study, and the
details of those variables are shown in Table 4.

Table
4: List of variables (Ibrahim, et al., 2017)

Variable
name

Definition

Categories

Overtaking category

Description of an
overtaking event characterized by risk of collision

0. Not
comfortable
1.Comfortable

Lane width category

Category of the lane
width

2. Less than 3 m
3. 3 m or wider

Presence of guardrail

0. No guardrail                                                                                                                1.
Guardrail on the right side
2. Guardrail on the
left side

Overtaking speeds

Maximum speed achieved
during overtaking

continuous

Front motorcycle’s
(FM) lateral position, X1

Distance of front
motorcyclist (FM) from the most left of edge line immediately before

Continuous

Participants’
proximity to the front motorcycle, X2

Distance of
participants from the front motorcyclist (FM) during overtaking event

continuous

Participants’ lateral
position, X3

Distance of
participants from the most right of edge line during overtaking event

continuous

The results of the study showed that roadside configuration and
lane width category tremendously affected participants’ overtaking speeds.

Chitturi and Benekohal in 2005 investigated the effects of lane
width on speeds of cars and heavy vehicles at work zones. Data were
collected at 11 work zones on Interstate highways in Illinois. One of the two
travel lanes in all of the work zones was closed. Four of the sites did not
have work activity. The width of the travel lane and the average free flow
speed (FFS) for each of the four sites were presented in Table 5. The information
regarding the four sites were  the hourly
volume, the percentage of trucks, the data used, the number of free-flowing
vehicles, and the variance in the FFS at each of the sites. Information
presented in Table 5 was used to obtain the values for speed reduction caused
by the narrow lane widths in the work zones.

Table 5:
Characteristics of different Sites (Chitturi and Benekohal, 2005)

As indicated in the table,
when the lane width was 16 ft in site 1, the Average FFS was 57.9 mph; however,
when the lane width was 10.5 m in site 4, the FFS was 47.2 mph.

Regarding the effects of lane width on passenger cars, trucks, and
all types of vehicles on FFS, Figure 1 shows the results.

Figure 1: FFS with variation in lane width for different vehicle
types (Chitturi and Benekohal, 2005

It is obvious from the above figure that there is a constant
decrease in free flow speed as the lane width decreases from 16 to 10.5 ft. When
the lane width is 10.5 ft, the average value of the FFS of heavy vehicles was
nearly 45 mph, and for passenger cars was 48 mph. As the lane width increaseed
from 11 to 12 ft, all vehicles speed increased with a constant rate.

Figure 2 shows speed reduction
in FFS for passenger cars, heavy vehicles, and all types of vehicles when the
lane widths were 10.5 and 11 ft.

Figure 2: Observed reductions in FFSs of vehicles in work zones (Chitturi
and Benekohal, 2005)

Passenger cars FFS reduction was smaller than heavy vehicles for
10.5 ft lane width. As the lane width increased to 11 ft, FFS for passenger
cars further decreased. Heavy vehicles FFS was reduced slightly compared to its
FFS reduction in 10.5 ft. From the collected data of the site, it can be
concluded that there is a greater reduction in speed of all vehicles as the
width of the lanes get narrower.

The FFS reduction values recommended in HCM for basic freeway
sections (4) and the reductions computed in this study were compared as
shown in Table 7.

Table 7: Observed Reductions in FFS for Work Zone

The FFS at site 1 (lane width of 16 ft.) was 3.5 mph greater than
the FFS at site 2. Therefore, the increase in FFS due to the wider travel lane was
set at 3.5 mph. Similarly, the decrease in FFSs observed at sites 3 and 4 were
the speed reductions caused by the reduction of the lane width.

The purpose of this comparison was to show that the HCM values could
not be assumed to be applicable in work zones. HCM does not indicate any
increase in FFS when the lane width is greater than 12 ft; therefore, a value
of 0 was used for the reduction recommended in HCM for a 16-ft lane. When the
lane width was 11 ft, the observed reduction of 4.4 mph was 133 % more than the
value of 1.9 mph recommended in HCM. When the lane width was 10.5 ft, the
observed reduction of 7.2 mph was 69% greater than the value of 4.25 mph
recommended in HCM. The conclusion is that the motorists reduced their speeds
more significantly in work zones than in a basic freeway section. When the
significant difference between the work zone speed reductions and the HCM speed
reductions were considered, it could be concluded that it would be wrong to
assume that the values for a basic freeway section in HCM are applicable in
work zones. Finally, it is recommended that the proposed values of FFS
reduction can be used at work zones.

Sharma, et al. in 2015 examined the “Safety and Operational Analysis
of Lane Widths in Mid-Block Segments and Intersection Approaches in the Urban Environment
in Nebraska”. To determine lane width effects on operational analysis, linear
regression models were used to examine lane width effects on the vehicles’
speed at mid-block segments. The Kolmogorov-Smirnov test was used as a statistical
tool to determine the effects of lane width on the vehicles’ headways in the
queue on the intersection approaches. The results of the study showed that lanes
with 9 and 10 ft. wide had higher speed in the central business district at 25
mph and areas outside of the central business district at 35 mph. Lower traffic
speed was also observed in the areas with 40 mph and 45 mph speed limits for
lane widths ranging from 9 to 10 ft.

Dixon, et al. in 2015 conducted a study about “reducing lane and
shoulder width to permit an additional lane on a freeway”. The research team
recognized the operational and safety implications of using reduced lane and
shoulder widths for a variety of freeway configurations. Data including speed,
crash, and geometric were used for freeways in Dallas, Houston, and San
Antonio. The research team observed an increase of about 2.2 mph in speed for a
12-ft lane when compared to an 11-ft lane.

Mecheri, et al. in 2017 studied “The effects of lane width,
shoulder width, and road cross-sectional reallocation on drivers’ behavioral
adaptations”. The research team aimed at investigating lane and shoulder width
effects on lane positioning strategies by examining vehicle distance from the
center of the lane. The researchers also aimed to assess the impact of the lane
width reduction, and shoulder widening on safety. The study was carried out on
a fixed-base driving simulator to find out how speed and lateral position are
affected by different lane width and shoulder-width combinations when the
Participants of the experiment were 34 drivers. Mecheri, et al.
concluded that reducing the width of the lane made participants drive closer to

Godley, et al. in 2004 studied the possibility driving speed reduction
by using lane delineation. A high-fidelity driving simulator was used on a
seven two-lane rural roads with lane widths of 3.6, 3.0, or 2.5?m, and with
either a standard centerline (control), a wide painted hatched road center
marking, or a wide white gravel road center marking. Taking 28 experienced
drivers resulted in speed reduction on the narrowest lane width road. Godley,
et al also concluded that the narrow lane width increased steering workload and
method for reducing driving speed was proposed by the research team. The method
was narrowing the lane width below 3.0?m by using a painted hatched road center
marking.

In 1990, Harwood investigated the” Effective Utilization of Street
Width on Urban Arterials”. The researcher noticed that lane widths of 10
feet or more resulted in accident rates. The results of the study showed that
narrower lane widths (less than 11 ft.) can be used successfully in urban
arterial street improvement projects where the additional space can be used to relieve
traffic congestion or address specific accident patterns. The researcher
recommended the usage of 10 feet lane on sections where the street can’t be
widened to improve traffic operations or lessen specific accident patterns.

Liu, et al. in 2016 tested the effects of lane width, lane position
and edge shoulder width on driving behavior for a three-lane underground urban
expressway. In the experiment, a driving simulator was used with 24 volunteer
test subjects. Five lane widths (2.85, 3.00, 3.25, 3.50, and 3.75 m) and three
shoulder widths (0.50, 0.75, and 1.00 m) were evaluated. The results from the
study showed that lane and shoulder width had substantial effects on driving
speed. Average driving speed increased from 60 km/h in the narrowest lane to 88
km/h in the widest lane. The results of the study showed that the narrower
lanes and shoulders widths, reduced speed and lateral lane deviation are
obtained. Besides the effect of lane width was greater than shoulder width.

Chandra and Kumar in 2003 investigated the “Effect of Lane Width on
Capacity under Mixed Traffic Conditions in India”. Data were collected at ten
sections of two-lane roads in different parts of India.  Total widths of the paved surface of the road
apart from its shoulders ranged from 5.5 to 8.8 m. Vehicles were divided into
nine different categories and after corresponding into passenger car units (PCU),
were valued at each road sections. The capacity of a two-lane road increased
with total width of the paved surface. Chandra and Kumar used the relationship for
deriving the adjustment factors for substandard lane widths.

4.
Conclusion

This paper briefly reviewed the studies of other researchers
regarding the effect of lane width on speed. The most significant outcomes are shown
below:

·
According
to Rosey’s study, speed of the vehicles were not influenced by the width of the
lane.

·
From
Ibrahim studies, it was concluded that speeds of drivers were greatly affected
by width of the lane.

·
Chitturi
concluded that reductions in FFS occur as the lane decreases from 16 to 10.5
ft. The researcher proved that HCM reductions in FFS are only applicable for
freeway but not for work zones.

·
According
to Sharma study, lanes with 9 and 10 ft. wide had higher speed in the central
business district at 25 mph and areas outside of the central business district
at 35 mph.

·
In
Dixon study, there was an increase of about 2.2 mph in speed for a 12 ft. lane
when compared to an 11 ft. lane.

·
In Mecheri
study, reduction in lane width caused participants drive closer to the center

·
Godley
proposed a new method for reducing speed by narrowing the lane width below
3.0?m using a painted hatched road center marking.

·
Ten
feet lane width was recommended by Harwood on sections where the street can’t
be widened for further improvement of traffic operations or minimizing specific
accident patterns.

·
Liu
concluded that lane width of highways had an enormous impact on driving speed.
The paper showed an increase in driving speed from 60 km/h in the narrowest
lane to 88 km/h in the widest lane.

·
From
Chandra studies, it was concluded that the capacity of a two-lane road
increased with total width of the paved surface.

References

·
American
Association of State Highway and Transportation Officials. A Policy
on Geometric Design of Highways and Streets. AASHTO,
Washington, D.C. 2011.

·
Rosey,
F., Auberlet, J. M., Moisan, O., & Dupré, G. (2009). Impact of narrower
lane width: Comparison between fixed-base simulator and real data. Transportation
Research Record: Journal of the Transportation Research Board, (2138),
112-119.

·
Ibrahim,
M. K. A., Hamid, H., Law, T. H., & Wong, S. V. (2018). Evaluating the effect
of lane width and roadside configurations on speed, lateral position and
likelihood of comfortable overtaking in exclusive motorcycle lane. Accident
Analysis & Prevention, 111, 63-70.

·
Chitturi,
M., & Benekohal, R. (2005). Effect of lane width on speeds of cars and
heavy vehicles in work zones. Transportation Research Record: Journal
of the Transportation Research Board, (1920), 41-48.

·
Sharma,
A., Li, W., Zhao, M., & Rilett, L. (2015). Safety and Operational Analysis
of Lane Widths in Mid-Block Segments and Intersection Approaches in the Urban

·
Dixon,
K., Fitzpatrick, K., Avelar, R., Perez, M., Ranft, S. E., Stevens, R., …
& Voigt, A. P. (2015). Reducing lane and shoulder width to permit
an additional lane on a freeway: Technical report (No.
FHWA/TX-15/0-6811-1). Texas A & M Transportation Institute.

·
Mecheri,
S., Rosey, F., & Lobjois, R. (2017). The effects of lane width, shoulder
width, and road cross-sectional reallocation on drivers’ behavioral
adaptations. Accident Analysis & Prevention, 104,
65-73.

·
Godley,
S. T., Triggs, T. J., & Fildes, B. N. (2004). Perceptual lane width, wide
perceptual road centre markings and driving speeds. Ergonomics, 47(3),
237-256.

·
Harwood,
D. (1990). NCHRP Report 330: Effective Utilization of Street Width. Transportation
Research Board, National Research Council, Washington, DC.

·
Liu,
S., Wang, J., & Fu, T. (2016). Effects of lane width, lane position and
edge shoulder width on driving behavior in underground urban expressways: A
driving simulator study. International journal of environmental
research and public health, 13(10), 1010.

·
Chandra,
S., & Kumar, U. (2003). Effect of lane width on capacity under mixed
traffic conditions in India. Journal of transportation engineering, 129(2),
155-160.