OVERVIEW OF DMRB VOLUME 6 ROAD GEOMETRY

DMRB Vol 6 – File 1

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VOLUME 6 - ROAD GEOMETRY Section 0:

NRA Introduction to Volume 6 (now withdrawn)

Section 1:

Links

Section 2:

Junctions

Section 3:

Highway Features

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VOLUME 6, SECTION 1: LINKS 4 No NRA Documents: NRA TD 9

Road Link Design.

NRA TA 43

Guidance on Road Link Design.

NRA TD 27 Cross Sections and Headroom. NRA TD10

Road Link Design for Type 2 & 3 Dual c/w’s c/w’s..

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VOLUME 6, SECTION 2: JUNCTIONS 1 No NRA Document: 

NRA TD 4141-42 Major/Minor Priority Junctions & Vehicular Accesses.

5 No NRA Addendum: 

TD 22 Grade Separated Junctions.

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TD 16 Roundabouts. Roundabouts

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TD 50 Signal Controlled Junctions.

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j Interchanges. g TD 39 Major

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TD 40 Compact Grade Separated Junctions.

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VOLUME 6, SECTION 3: HIGHWAY FEATURES 2 No NRA Documents:  NRA TA 69

Location & Layout of LayLay-Bys (under review and will b become a standard). t d d)

 NRA TA 70

Location & Layout of Services Area.

3 No NRA Addendum:  TD 36

Layout & Dimensions of Subways.

 TA 66

Police Observation Platforms.

 TD 51

Segregated left left--Turn Facilities & Subsidiary Deflection Islands at Roundabouts.

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NOT IN VOLUME 6 NRA TD 19 SAFETY BARRIERS THIS IS IN VOLUME 2 (BRIDGES) SECTION 2

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NRA TD9/07 AND NRA TA 43/03 ROAD LINK DESIGN

DMRB Vol 6 – File 2

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INTRODUCTION  Background to Road Link Design  Design Speed  Relaxations and Departures  Sight Distance  Climbing Lanes  Horizontal & Vertical Alignment g Carriageway g y Design g  Single  Dual Carriageway Design  Local Roads

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BACKGROUND TO ROAD LINK DESIGN  Design D i St Standard d d TD9/81 iintroduced t d d iin UK iin 1981 contained t i d radical di l features based on research (In 1984, TA 43/84 as published)  Design Standard TD9/93 replaced both the above documents in 1993  NRA TD9/07 is based on TD9/93  NRA TA43/03 is based on TA43/84 and is included to provide the background information (Is now out of date and may be withdrawn)  A major objective of these documents was to ensure that designs achieve value for money without any significant effect on safety, by pro iding greater flexibility providing fle ibilit in difficult diffic lt circ circumstances mstances  Standard applies to  All National Roads  All Roads affected by National Road Projects (Clause 0.8)  For Regional and Local Road Schemes, designers should confirm the road standards to be used with the Roads Authority (Clause 0 0.9) 9) 8

DESIGN SPEED: CONCEPT  Drivers regulate their speed along a road in accordance with the speed characteristics of the length of road over which they have just driven and their perception of what lies ahead  The Design Speed is the estimate of the speed traffic will adopt, for given alignment and layout constraints  There is typically a wide range of vehicle speeds on a given section of road, and the Design Speed is defined as the 85%ile speed, i.e. the speed which is exceeded by 15% of drivers  The development of the geometric parameters based on given Design Speeds (Stopping Sight Distance, Full Overtaking Sight Distance, Horizontal & Vertical Curvature and Superelevation Superelevation)) took account of the 15% of drivers who will exceed the Design Speed

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NATIONAL ROAD DESIGN SPEED: DETERMINATION  The determination of Design Speed is a “reactive” process  It recognises that, if a road alignment needs to be bendy for environmental i t l or physical h i l reasons, th the curvature t and d visibility i ibilit standards can also be lower, reflecting the lower speed traffic will adopt in any case  For the higher standard National Road, it generally produces “expected” values  Each Design Speed is divided into Bands A & B in order to avoid a “sudden jump” in standards at the “changeover points”: more flexibility in design is available in each Band B p limits of 60kph p or less will apply, pp y, the  However,, if mandatoryy speed Design Speed is selected by reference to the proposed speed limit (see Table 2 of TD9)

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NATIONAL ROAD DESIGN SPEED: DETERMINATION  Two parameters are used when calculating the Design Speed  Alignment Constraint (Ac) – measures the degree of constraints imparted i t db by th the road d alignment li t ((e.g. b bendiness di / visibility) i ibilit )  Ac for dual c/w’s = 6.6 + B 10  Ac for single c/w’s =

12 – visi + 2B 60 45

 Layout Constraint (Lc (Lc)) – measures the degree of constraint imparted by road cross section / verge widths / frequency of junctions and accesses. (Table 1 in Chapter 1 gives the Lc value).

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NATIONAL ROAD DESIGN SPEED: EXAMPLES

V50 wet

Layout Constraint Lc Kph

V85 wet

Mean Spee ed of Light Ve ehicles Kph (w wet)

DESIGN SPEED 120

100 0

A 120 Kph

5

90

B

10

100

15

80

A

20

B

25

85

70

A

30 60

Single C/ways A c FOSD/4 plus 20% with warning lines FOSD/2 in advance) 59

SINGLE CARRIAGEWAY DESIGN: WAYS TO IMPROVE OVERTAKING VALUE  Modify the junction strategy by stopping up, diverting or bridging side roads  Adjust Adj t the th alignment li t to t produce d more straight t i ht sections ti  Introduce climbing lanes on hills previously not considered justified  Introduce roundabouts at the more heavily trafficked priority junctions to enable sharper changes of direction  Introduce sections of S4 or dual carriageway

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DUAL CARRIAGEWAY DESIGN

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DUAL CARRIAGEWAY DESIGN: PRINCIPLES  With no need for the discrete “overtaking sections” and “non“nonovertaking sections” of single carriageways:  the th d design i off d duall carriageways i ttypically i ll iinvolves l th the optimisation ti i ti of flowing, aesthetic alignments  there are no limitations on the use of horizontal and vertical curves in excess of one step below Desirable Minimum  The design should permit light vehicles to maintain the Design Speed  A smooth flowing alignment is required for sustained high speeds

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DUAL CARRIAGEWAY DESIGN: PRINCIPLES  Large radii curves rather than straights will produce a flowing alignment. Short curves and straights should not be used.  Adjacent Adj t curves should h ld b be off similar i il llength th  Curves of the same or opposite sense that are visible from one another should not be connected by a short straight  Small changes in direction should not be made as they give the view of the road ahead a disjointed appearance  Changes in horizontal and vertical alignment should be phased to coincide wherever possible  Embankments and cuttings should not make severe breaks in the natural skyline  When crossing a ridge in cutting or passing through woodland, the road should be on a curve where possible so as to preserve an unbroken background b k d 63

DUAL CARRIAGEWAY DESIGN: APPLICATION OF PRINCIPLES  These principles are generally desirable for all dual carriageway designs  However, H ffor llower ttraffic ffi flflows, a hi high h standard t d d off aesthetic th ti d design i may not be justifiable, particularly where the dual carriageway represents an alternative to a single carriageway  If designed as an at at--grade alternative to a single carriageway, a dual carriageway will frequently demonstrate superior economic performance to a single carriageway at flows well below the upper li it off single limits i l carriageway i demand d d fl flows.

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DUAL CARRIAGEWAY DESIGN: EMERGENCY ACCESSES  Such accesses maybe either  Break in the central reserve barrier as an Emergency Crossing Point P i t (ECP)  An Emergency Access Link (EAL) to connect to the local road network  Clause 8.15 to 8.36 gives details of the ECP and EAL

Minimum Frequency for Emergency Access Provision

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NRA TD 10/07 :Road Link Design for Type 2 and Type 3 Dual Carriageways.

DMRB Vol 6 – File 3

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TYPE 2 AND 3 DUAL CARRIAGEWAY  Type 2 – A divided all all--purpose road with two lanes in each direction divided by a barrier.  Type T 3 – A divided di id d allallll-purpose road d with ith ttwo llanes iin one di direction ti and one lane in the other direction divided by a barrier.  Type 2 is the preferred road type for offline alignment.  TD10 should be used in conjunction with TD9  Table 4 of TD 9 gives recommendations on capacities / junction treatments etc. etc

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TYPE 2 AND 3 DUAL CARRIAGEWAY Recommended Rural Road Layouts (ex Table 4 of TD9)

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TYPE 2 DUAL CARRIAGEWAY  Cross section as per TD 27.  Replaces to wide single c/w’s in the old standard  Alignment as per dual carriageways (no FOSD requirements).  Junctions to be either;  Roundabouts. Roundabouts  Compact Grade Separation.  Left Left--in / Left Left--out.  Vehicular Access;  Avoid if possible.  Left Left--in / Left Left--out.

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TYPE 2 DUAL CARRIAGEWAY  Verges on Type 2 Dual should be designed to accommodate broken down vehicles  ECP and d EAL are nott required i d but b t EAL may be b provided id d if there th are suitable locations  Direct vehicular access should be avoided where possible  Facilities for nonnon-motorised users to be provided as necessary (no breaks in the central reserve barrier)

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TYPE 3 DUAL CARRIAGEWAY  Cross section as per TD 27.  Alignment as per dual carriageways.  Passing lane lengths / changeovers.  Junction Strategy;  As per Type 2 plus  Right turn priority junction with Ghost Island.  “U” turn facilities.

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TYPE 3 DUAL CARRIAGEWAY – SCHEMATIC LAYOUT Schematic Layout of a Type 3 Dual Carriageway

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TYPE 3 DUAL CARRIAGEWAY – U TURN OPTIONS U-Turn Loop on Minor Road

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LUNCH

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