Proclaim arterial routes for urgent upgrade to free flowing status
The first and main cause of traffic delays in Port Elizabeth is that arterial routes are not treated as high mobility routes. Alternatively stated, Port Elizabeth's arterial policy favours "access to land" over "mobility" (SANRAL 3.8.4).
A random access policy exists, that creates the need for cross town traffic to stop at all intersections. Secondly right turn movements are allowed at all intersections which reduces green time for through traffic, and thirdly the random addition of extra signals is allowed each time a new development or focus point seems to justify it
In the Joubert Plan suggestions are made to firstly adopt a new policy of recognition of arterials as no stopping roads and then apply some innovative concepts to keep cross town traffic flowing, for which he has proposed the "four keys to continuous flow"
Another issue of concern to Joubert, over which he has written previously, is that there is a heavy focus on traffic calming devices in stead of addressing the underlying problem of inefficient main routes. Frustrated drivers take speeding shortcuts through residential areas to avoid lengthy waits at red lights along arterials.
Joubert's main focus is on continuous_flow_methods, and he has proposed the "four keys to continuous flow",
that include free left turns, indirect turns (turn left to go right) and one-way streets.
The "right of way" traffic sign below, that is common in some countries, and intended to coax traffic to keep moving, should be widely introduced and planning done around it
The Port Elizabeth map accessible from the left hand upper corner on this page shows a schematic of PE's arterials and main bottlenecks for reference
free left turns
Free left turns coupled with restriction of right turns at intersections and the left in / left out rule is an essential element in speeding up traffic flow
A good example of a working free left turn lane, also called a slip lane by some, is at the left turn from William Moffet south into Walmer Main Road east.
Another is from Kragga Kamma south into Circular Drive east, in the upgraded intersection at the wash-away bridge.
However, similar lanes should have been built, but were not, at the same intersection, for Kragga Kamma north, and Circular into Kragga Kamma west.
Also, a free left turn should have been provided from 17th ave into Buffelsfontein east.
And one should have been provided at Harrower west into Kempston south. In this case it seems like they wanted to do it, because a channel was actually provided for the left side lane of Harrower, but it serves no purpose where it is. It should have been rather placed in Kempston south, as part of a free left turn scheme.
There are many more places where free left turns can be applied. Where they do exist, it seems they were placed there more by accident than by design, because there is no policy for free left turns. The "Left-turn-on-red-after-stop" rule would further allow free left turning (see below) but this time under driver control, like it would have been in the days of simple stop signs
Continuous flow (green) at T-junctions is a feature that allows one of the directions at a T to flow continuously. This is a cheap and easy way to eliminate an unnecessary red light. An existing example is Harrower west at the exit into Prince Alfred.
Two very obvious locations for this feature is in Buffelsfontein east at the Builders Warehouse. All that new road width was provided, but the flow was not improved. Two additional unnecessary signals were provided and the free left turn above was not allowed. Three opportunities for free-er flow were missed. This link takes the reader to the median U turn proposal by this author that shows how the signals at Buffelsfontein could have been avoided
Left-turn-on-red-after-stop is a practice widely applied in more advanced environments. Under the prevailing perception in the NMBM that speeding and reckless driving is out of control, such a rule is likely to meet instant opposition. However, those drivers most targeted for said prevailing perception, the villified taxi drivers, are already practising this manouvre, which is actually quite safe if applied responsibly, and should be allowed
roundabouts, indirect turns and selected one-ways
Here are some suggested continuous_flow_methods and proposals for various areas in Port Elizabeth where these can be applied.
All types of continuous flow intersections spring from the concepts found in a Roundabout. The roundabout is easiest to understand because of the simplicity of it's form, and it has been touted as a panacea (cure-all) to all traffic problems by some.
The Roundabout is a form of indirect turn that allows continuous flow while main streams cross in a weaving action. Roundabouts are effective if correctly applied to appropriate intersections, and are commonly used in many countries, but they also have limitations and are cautiously used or avoided by some authorities.
SANRAL section 6.6.2 does not provide a great deal of information on roundabout design and sounds some of the cautions.
In low to medium traffic densities roundabouts compete in principle with fourway stops, which work well, cost less, and are safe, so some will say why bother with a roundabout.
The largest car user in the world, the USA, has historically had very few roundabouts. In recent years the US FHWA has been conducting in-depth studies on the use of roundabouts in other countries and has published a large amount of information there-on.
One of the FHWA conclusions is that philosophies regarding roundabouts differ in different countries. In one group of European countries rapidity of flow is the main criterion, in another group, traffic calming is the main objective
Regarding continuous flow at high volumes, the main problem with roundabouts relates to capacity. While various features may be incorporated to maximise capacity, like entry and exit configurations, and the number of circulatory lanes, capacity is ultimately limited by the length of the circulatory path, controlled by the inscribed circle, which in urban locations tends to be a fixed.
Capacity in large flow environments is difficult to assess due to the large number of input variables. Click on the pic adjacent (96 kb) to enlarge to see the number of input variables.
Roundabouts need lots of space, especially in built up areas where space for roundabouts was not allowed for in original planning. Once built roundabouts are not easy to expand, if found to be under-capacity
When roundabouts run out of capacity they cause a type a gridlock of their own and attract traffic signals. The entire object of continuous flow is then negated. A sad example is the two large roundabouts at the bottom of Heerengracht in Cape Town, which now have 5 traffic signals each, to controll the massive flow of traffic in that area.
In assessing the various bottlenecks in Port Elizabeth where arterials cross, conventional roundabouts do not appear to offer immediate solutions, although they do need to be considered in the spectrum of alternatives.
The roundabout concept of continuous flow, where traffic streams cross in a weaving pattern, can be employed in other polygonal geometric layouts, layouts of various shapes that are not pure circles. In such layouts circulatory paths are longer than is possible in a roundabout and weaving is allowed to take place over greater distances. These cases allow application of the roundabout concept within the contraints of existing built up areas.
These geometric layouts described next, that can be applied in Port Elizabeth, are:
- The median U-turn (MUT) (indirect turn)
- One way streets
The median U-turn type of indirect turn , turn-left-to-go-right, is similar to a roundabout in terms of the way flows of traffic cross, but as it can be spread out over any distance along an existing road, it offers a longer circulatory path on which weaving can take place and thus higher capacity. The MUT is seen as "unconventional" by many and has not been applied widely to achieve its maximum potential. It can be used to advantage in Port Elizabeth in a number of places
The median U-turn overcomes the need for otherwise mandatory right turn signalised intersections. The sketch shows the median indirect turn
Go to Intersection Design Elements for a full description of this concept
One Way Streets
The sketch shows traditional two way routes. Comparing the number of stops "red" with the one below will show how much easier traffic flow is when based on one way routes. download pic 38kb
Advantage of one way
When two major streets run parallel to each other, traffic flow is improved by converting the two streets to opposing one ways. Side entry from minor streets will be according to the left in left out rule Entry from minor streets would need to be adapted to get the best advantage from the one way conversion with appropriate markings and channelization. Local traffic from a minor cross street wishing to make a right turn would make an indirect left turn, weave through the left moving stream, exit at the next cross street and effetively drive round the block to enter the right moving lane.
download pic 45kb
Areas where one-way conversions can provide easy relief are:
- Fettes road east / Harrower road west - vital for 2010
- Heugh road west / Villiers road east
- Walmer main road west / Church road east
- Newton Park miscellaneous business streets
Harrower and Fettes roads can be made opposing one ways, eliminating three traffic signals and allowing continuous flow along this part of an important arterial route.
Villiers road can be made into a one-way, and have all the stops removed to make this the main arterial running east from south western areas. Heugh road can be made into the opposing parallel one-way running west, with signals removed. No additional paving will be necessary, except at entrances and exists and some chanellization. Options for entry and exit from Villiers road exist and will be shown later. Re local impact of a through road, in this area, there may be some objections, but access to property will not be affected. The western part of Villiers is residential, the eastern part is becomming mainly business. In this part of town children dont play cricket in the streets so the increase in risk to residents is negligible. Its an anomoly that this double carraigeway is not part of the main transportation system. Click on pics to enlarge
Church road can be made into a one-way east with Main road the opposing parallel running west, with signals removed along Main road at 9th 10th and 14th avenues. No additional paving will be necessary, except at entrances and exists and some chanellization. Entry from main road will be by left turn into 14th then right into Church. Exit will be into 8th avenue, for which no specific proposals are made here-in. Re local impact of a through road, in this area, there may be some objections, but access to property will not be affected and it is doubtfull if traffic noise will become unacceptable in this spacious area. In this part of town children also dont play cricket in the streets so the increase in risk to residents is negligible. Its a feature of old Walmer that this wide road space exists which can become part of the main transportation system with very little cost.
Less easy but should be evaluated
- Diaz road to integrate with Harrower and Fettes with one-way elements
- Durban road to integrate with Highfield or Stanford
- Other areas to be studied and defined eg
- Govan Mbeki has for years had a very popular parallel street viz Swartkops street running next to the railway line, that carries a lot of traffic because there are no stops until it reaches Grahamstown road, but this route has never been formally integrated. It is a good example of how much traffic a road without stops can carry
develop arterials - suggested rules for
To improve the flow of traffic on existing roads we need to
- Recognize and re-assert the need and importance of arterial routes
- Proclaim arterial status for the main routes and set policy guidelines for arterials
- Recognize that most of the traffic we see sitting at traffic signals is long distance traffic with no business at that point
- Recognize that through traffic stops continuously for the benefit of local traffic
- Recognize that local traffic should not have random access to arterial routes
- Reduce the number of random access points to arterials as we have today
- Recognize that right turn movements are the main problem causing slow-down of traffic
- Reduce the number of traffic signals and number of stops along arterials
- Develop and select suitable "intersection treatments" for each case
arterials suggested policy guidelines
Arterials can be defined as limited access routes designed to move large volumes of traffic over medium to long distances at a high Level of Service LOS. Arterials have certain elements in common with freeways, the main difference being that intersections are at ground level (AT grade) and flyovers are not a main feature.
The following are the main elements suggested for a set of arterial policy guidelines in the NMMM area.
- Proclaim arterial status for the main routes around the city, most of which already carry an existing M route number
- Clarify road reserves around these main routes
- Project future traffic volumes for all arterials
- Evaluate adequacy of road reserves for future needs against traffic volume projections.
- Update this record on a continuous basis to include traffic effect as new building construction is approved
- Take urgent action to expand road reserves where seen to be insufficient
- And / or place moratoriums on new construction where future road space may be under threat
- Achieve safe 80 km speed limits on arterials by (period schedule to be established)
- Prohibit direct right turns on arterials
- Adopt a LEFT-IN / LEFT-OUT rule for arterials
- Develop high speed access and exit lanes on arterials according to SANRAL geometric rules
- Employ innovative concepts for M route intersections
- Create indirect turn arrangements for right turning traffic
- Create one way layouts for major streets
- Use city blocks as roundabouts
The conflicting issues around speeding up and slowing down traffic needs to be settled. The many emotional reactions to lawlessness among taxi operators should not be allowed to reduce the objective of high speed arterials, the taxi issue should be dealt with on a traffic law enforcement basis, or as per the Public Transportation Action Plan which will cut their wings if they cant play according to the rules.
The NMMM plans for
SANRAL geometric manual - notes re
SANRAL's Geometric Design Guidelines (hereinafter referred to as SANRAL) describes various types of intersections. This does not mean, however that SANRAL should be seen as an exclusive bible, because SANRAL's jurisdiction is not present on all urban routes (SANRAL - Introduction page 1.1) and SANRAL was compiled using other similar existing multi-national references with some material from said sources either modified or not included. SANRAL is a living document and will be updated from time to time. SANRAL is practical and at the same time highly theoretical. It contains a wide spectrum of standards. Much of the material is conceptual discussion and the selection and use there-of needs to be done with care to ensure appropriate analysis, parameters and standards are applied in each case. SANRAL does NOT say what is best for any specific case, the final interpretation and selection is up to the reader.
The descriptions below are not necessarily from SANRAL, but SANRAL is referred to where applicable. The median U-turn which features heavily in Joubert's suggestion is not in SANRAL. The suggestion of median U-turns and one-way conversions represents "out of the box" thinking, encouraged by the leaders in this game.
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