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DOCS NRA-#384363-v10-Policy Design Guideline …

::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 1 of 13 04/05/2009 Design GUIDELINES FOR single carriageway NATIONAL ROADS First Draft May 2009 Planning and Design Cluster ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 2 of 13 04/05/2009 Index 1 Preamble: ..3 2 Classification: ..3 3 Level of Service and Capacity: ..4 4 Typical Road Cross-sections: ..4 5 Intersections: ..6 6 Warrants for Interchanges: ..6 7 Super Routes: ..8 8 Road Reserves and Land Acquisition:..8 9 Road Safety Audits: ..9 ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 3 of 13 04/05/2009 Design Guideline standards for single carriageway National Roads Design (General): 1 Preamble: A substantial portion (over 90%) of the National Road Network (SANRAL managed) consists

::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 3 of 13 04/05/2009 Design Guideline Standards for Single Carriageway National Roads Design (General):

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Transcription of DOCS NRA-#384363-v10-Policy Design Guideline …

1 ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 1 of 13 04/05/2009 Design GUIDELINES FOR single carriageway NATIONAL ROADS First Draft May 2009 Planning and Design Cluster ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 2 of 13 04/05/2009 Index 1 Preamble: ..3 2 Classification: ..3 3 Level of Service and Capacity: ..4 4 Typical Road Cross-sections: ..4 5 Intersections: ..6 6 Warrants for Interchanges: ..6 7 Super Routes: ..8 8 Road Reserves and Land Acquisition:..8 9 Road Safety Audits: ..9 ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 3 of 13 04/05/2009 Design Guideline standards for single carriageway National Roads Design (General): 1 Preamble: A substantial portion (over 90%) of the National Road Network (SANRAL managed) consists of single carriageway (2, 3 or 4 lane) roads.

2 It is likely that over 50% of these roads will have Design standards less than the desired 120km/h, being roads that were previously considered of a lower order and/or were designed and constructed before the 1970 s. Substantial lengths of these roads could still satisfy the minimum standards for a 120km/h Design speed, while significant portions may not. Upgrading all such portions to 120km/h or even a 100km/h Design speed is often found to be impracticable and likely to be unaffordable and not economically justifiable.

3 In addition most of the lower order of the national network carry substantially less traffic than the higher order N routes and is likely to do so for the foreseeable future. Designers are reminded that Design speed is a theoretical Design parameter and must not be confused with actual operating conditions or even worse, posted speed limit restrictions. Hence, designers must develop appropriate Design solutions for such lower order roads which may include widening of paved width or cut faces where sight distance is not optimal, introduction of transition curves and increased super elevation.

4 Warning signs and optical devices where current operating conditions fall below the generally perceived desirable safe operating conditions Designers are encouraged to use sound engineering judgement while ensuring that acceptable operating conditions can be maintained and future upgrading of such facilities can be accomplished in a rational and cost effective manner. Designers and project managers are required to ensure that the distinction between the Design speed parameter and operating speeds and posted speed limits are adequately explained and addressed in all documentation.

5 Designers are well advised to consider alignments that will be pleasant to the motorist to drive on. The motoring experience must be enhanced. For this reason this consideration and its application must be discussed in Design reports. 2 Classification: It is a requirement that SANRAL s roads shall be classified in accordance with the DoT s new RIFSA classification available from DoT or DoT website. The majority of SANRAL s network will fall into Class 1. It is intended that such roads shall be upgraded and constructed to the minimum preferred National road standards as far as practicable.

6 The remainder of the network will fall into Class 2. It is intended that reduced standards could be tolerated on such roads depending on traffic volumes, now and in the future. However, SANRAL will also as part of its community development programme construct Class 6 and 7 roads from time to time. Typical ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 4 of 13 04/05/2009 Design details for such roads are included in the SANRAL s typical drawings. 3 Level of Service and Capacity: Detailed LOS and capacity upgrade requirements must be determined with the Follower Density procedure simulation model.

7 Indicative table of trigger volumes (AADT) for various terrain types and heavy vehicle proportions of the traffic stream are contained in tables 1 and 2. Designers shall take note that the tables are based on using particular peak factors and directional flows. These particular factors are based on research on SANRAL s existing national road network and have a significant impact on the trigger volumes. 4 Typical Road Cross-sections: 2-lane roads ( single carriageway ): (a) Roads with AADT larger than 3000 vehs/day (AADT): Shoulders are paved and have a minimum width of Where traffic is to be accommodated during upgrade and rehabilitation work, the paved width should be a minimum of m ( lane + paved shoulders).

8 Where traffic volumes are less than 2000 vehs/day and likely to remain below 3000 vehs/day for next 10 years a narrower cross section may be considered. However, in all cases toll roads should have paved shoulders of at least , distinguishing them from non-toll roads. (b) Roads with AADT of less than 3000 vehs/day in 10 years: Paved shoulder: 800mm (min), 1000mm preferred Total shoulder width (including gravel): excl. rounding Lanes (min), Preferred Paved Width: (min) Preferred carriageway Width: min for existing, preferred incl.

9 Rounding Bridge structures: width between barriers (Preferred). Retain existing width if practicable and safe. Each case to be motivated accordingly. V-drains to be outside of wide carriageway . Shoulders to be paved where side drains are installed (Cuts and high fills). 3-lane roads ( single carriageway ): These include sections of higher order or wide 2-lane roads that have been re-marked to alternate 2 lanes with 1 opposing lane configuration over its entire length, the length of the alternate configurations being including tapers leading directly into a similar but opposing section.

10 Research appears to indicate that this configuration could be more dangerous than the conventional 2-lane configuration (although there are also success stories). The substantiation is as follows: It has been found that operating conditions LOS/capacity is not substantially improved. ::ODMA\PCDOCS\DOCS_NRA\384363\10 - DRAFT 5 of 13 04/05/2009 Areas of conflict are introduced where there were none previously at the merge of the 2 lanes Leads to platooning. Leads to excessive speeding in the 2-lane sections.


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