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the realities

environment and energy
the trade off
DME campaign
growth and congestion
the calf path
road reserves - where are they
silent cops or silent executioneers

what to do

continuous flow methods
intersection design
lev el of service
context sensitive design
ways to reduce congestion toolbox
2007 comments re NMBM dedicated bus routes
2011 quo vadis BRT
letters and press articles


Suggested Plan for Buffelsfontein/17th Ave zz
Sugges ted Plan for Walmer Heugh and Main Roads
S uggested Plan for Walmer Blvd / M4
Sugges ted Plan for William Moffat Expressway
Suggested Plan for Fairview By Pass
Sugge sted Plan for Walmer Park / Main Road
Suggested Plan for Uitenhage Road / N2
Suggested Plan for Stanford Rd / N2
Suggested Plan for Disa Ave / N2
Suggested Plan for Circular Drive and Kragga Kama
Suggested Plan for Samantha Rd / N2


By Pierre Joubert

Survey | SEO

Level of Service (LOS)

The average road user will tolerate a certain level of congestion and delay before becoming frustrated or annoyed or attempting unsafe driving manoeuvers.

To address the issue of acceptable degrees of congestion, the level of service concept has been developed. The various levels have been subjectively determined and quantatively described. (1)

From various USA references, the Level of Service (LOS) of a road is categorized from "A" to "E", where "A" is excellent and "E" is terrible. On the internet examples of these definitions can be found. (2)

Simply put, from the individual's side, everyone wants to get to their destinations faster. From the society viewpoint, we need efficient roads to grow the economy. More and more today we also need to avoid wasteful use of fuel on inefficient roads. For those reasons we all want to see road congestion cleared. However, to provide improved level of service (LOS) money needs to be spent with that as an objective and certain TRADE-OFFS need to be made.

The buzzwords "context sensitive design" and "multi-criteria matrix appraisal framework" are also used alongside LOS in both SANRAL and ASSHTO's geometric design guidelines to describe this tradeoff process, which is intended to take all factors into consideration before any decisions are made.

While SANRAL's Geometric Design Guidelines is a very comprehensive document, it is also highly theoretical with long passages taken from the AASHTO big daddy, and for the designer at the coal face I dont believe it is of much use when the pressure is on. A subtlety like LOS will not be part of the decisions taken unless it is a policy requirement from a higher level, like DOT, and it was clearly absent in the NMBM BRT planning

The trade-offs

The recommendations here-in contained center mainly around suggested changes to existing geometric layouts so that bottlenecks are removed and continuous flow of traffic along arterial routes can be achieved. This will include a redefinition of arterial routes and limiting access to arterial routes.

However this will be easier said than done because of obstacles that have grown over time, such as layouts we have inherited via the wagon trails and calf paths of the past, and trade-offs that need to be made, for example

  • If we want to speed up traffic flow, safety will be seen as compromised by some
  • If we want to speed up trafic flow we have to deal with traffic_calming issues
  • If we are going to favour through traffic over local traffic, we are going to inconvenience some people doing short local trips
  • If we want space to expand roads, we have to curtail some property development, and perhaps buy up some properties that are blocking the way
  • If we are to develop arterials we might have to cut through some quiet parts of town
  • If we want to limit access to through roads (arterials) we also limit access to property
  • And if we are going to do our share as a community towards energy consumption and global warming, we better stop burning unneccesary fuel, even if today as individuals we can still afford to do so

These trade-offs must be seen as growing pains and balanced out against each other. The concept "level of service" LOS is thus used to arrive at goal posts for planning, and attempts to guide this balancing process.

References Minnesota DOT Road Design Manual
(1) Section 2-5.08.04 Level of Service
(2) Table 2-5.08 Level of Service By Highway Type

Survey | SEO


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