Category Archives: Congestion

Safer urban car lane widths

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Readers need to be aware that this post does have a bias toward giving weaker road users a higher priority for road space. My reading of these design manuals is therefore to identify the widths providing greatest benefit for people aged 8 to 80.
First warning: For this post, lane width is about the distance between painted lines or changes in road surface texture. Kerbs/road bumps greater then 50mm in height limit the available options. See the photo at the end of this post.

New Zealand legislation states that a “lane for the use of vehicular traffic … is at least 2.5 m wide” Reprinted 1 October 2017 – Land Transport (Road User) Rule 2004 (SR 2004/427)

Here is an example (in Schiedam) of narrowed motor vehicle lanes with the cycle lane width being maintained through the intersection. As we can all see, this doesn’t mean excluding heavy traffic (note bus stop). What it does mean is that the safety* a cycle lane width gives can be continued through the intersection.

*“Cycle lanes … provide a modest 10% safety improvement for cyclists, but 30% for pedestrians” This is from the NZTA Pedestrian planning and design guide Table 6.3

Data collected from the Minneapolis-St. Paul and Oakland County – Detroit areas does not support the idea of wider lanes being safer for motorists.

“There is no indication that the use of 3.0- or 3.3-m (10- or 11-ft lanes), rather than 3.6-m (12-ft) lanes, for arterial midblock segments (& arterial intersection approaches) leads to increases in accident frequency.” P23 (P25)

Ref: Relationship of Lane Width to Safety for Urban and Suburban Arterials – 2007 by Ingrid B. Potts, Douglas W. Harwood, and Karen R. Richard

Measures from Tokyo & Toronto also do not support wider lanes being more efficient for motorists. Ref: Narrower Lanes, Safer Streets – Dewan Masud Karim – 2015

Impact on Traffic Capacity and Congestion:

“Contrary to common belief, the results clearly demonstrate that narrower travel lanes, particularly 3.0m lanes, carry the highest traffic volumes (18% higher compared to 3.5m lane) … there is no measurable decrease in urban street capacity when through lane widths are narrowed from 3.7m to 3.0m … Traffic delays on urban roads are principally determined by junctions, not by midblock free flow speeds” p12

Large Vehicles and Narrower Lanes:

“Low volume trucks (less than 5%) experience no operational problems for narrower lane widths … For buses, it suggests using 3.3m for mixed traffic conditions and 3.0m where buffered bicycles lanes exist” p13

Lane widths to avoid – From Handbook for cycle-friendly design by UK based Sustrans 

“Avoid widths between 3.1 and 3.9m” p17

“Bus lanes widths … 3.2m to 3.9m to be avoided” p19

In my opinion it is particularly important that when narrowing lanes that kerbs and speed bumps are kept as low as possible. People stop for a variety of reasons. Bumps can make the ride in a bus uncomfortable or an ambulance trip worse than it needs to be.

Photo Gottingen – Lange Geismar Str

Past Blog post on lanes

A good one way cycle lane width = 2m+

4 lane roads when to

Lane width and cars per hour per lane

Number of cars per lane

Hamilton’s Traffic change last 3 years

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From: Council meeting Wed 6th Dec 2017 – 2018-28 10-year Plan – page 69, line 37

Drivers of significant expenditure variances include “Over the last three years we have seen a 15% traffic growth on main routes, Hamilton is now the “busiest” Council traffic network in the country (based on VKT/km)”

It is true that traffic volumes are growing, but when this is mapped the growth decreases along main routes through Hamilton.

Another way to see change in growth is to graph traffic counts; (you can find data here –  Link) It is presented as a pdf not as live Excel, so after a bit of copying and typing , we have a graph that shows a trend line of traffic growth on State Highways, which are central government funded, and reducing traffic on local roads, which are partly funded from local rates.

Traffic counts are not the only way to measure changes in traffic volumes. At the same Council meeting Wed 6th Dec 2017  – page 69, line 37

“Hamilton is now the busiest council traffic network in the country (based on VKT/km)”

When asked, the very helpful staff at council added a bit more detail to this VKT/km.

‘The busiest Council traffic network information is from the One Network Road Classification tool which has been developed for Road Controlling Authorities. Hamilton City measures 1,272 VKT/km compared to Auckland at 1,136 VKT/km and Tauranga City 1,066 VKT/km.’

There seem to be numbers that support the idea traffic volumes are growing, but the opposite may also be true; looking back to past post on  Parking evidence, vehicle counts in Hamilton central appeared to be decreasing.