Motorway Interchanges

Motorway Interchanges

2013 edition - Version amended in May 2015 - 2021 Update


This guide supplements ICTAAL 2000, the National Instruction on Technical Design Requirements for Rural Motorways (Instruction sur les Conditions Techniques d’Aménagement des Autoroutes de Liaison).

It provides road designers with additional information concerning the general design and geometric characteristics of motorway interchange layouts and access to ancillary areas on interurban motorways.

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Motorway Interchanges

It introduces a few changes with respect to ICTAAL 2000 and supersedes Factsheets nos. 22 and 32.

The new provisions in this guide are included in the consolidated version of ICTAAL published in May 2015 and cited in the French government Instruction of 13/07/2015, superseding the original version issued on 12 December 2000.

This guide is itself cited in the government Instruction of 13/07/2015, and as such, is considered to be an "instruction" applicable to the national road network. However, local and regional authorities may refer to the guide, which has been designed for use by all motorway and assimilated road network managers developing projects for which they will be the contracting authority.



1 - General Design 

  • Traffic considerations 
  • Motorway forks or nodes 
  • Grade-separated interchanges between a motorway and an ordinary road 

2 - Visibility* 

  • Principal sight distances 
  • General provisions 
  • Visibility on approaches to access points 
    Visibility at an exit 
    Visibility at an entrance
  • Visibility along slip roads and branches 
  • Visibility under structures

3 - Geometric Characteristics of Branches and Slip Roads 

  • General provisions 
    Minimum and maximum radius values 
    Sequencing of horizontal alignment elements 
    Transition curves 
    Transverse deflection length 
    Deceleration and acceleration zones* 
  • Vertical alignment
  • Cross-section
    Interchanges between a motorway and an ordinary road 
    Auxiliary lanes 
  • Crossfall 

4 - Exit Systems

  • 4.1 - Exit from the mainstream lane
    Choice of exit system*
    Layout of direction signs and markings*
    Single-lane exits 
    Two-lane exits
    Left-hand exits (on nodes only)* 
  • Lane reduction after an exit
  • Exit from a slip road or branch
  • Exit system geometry*

5 - Entrance Systems

  • Entrance onto the mainstream lane
    Choice of entrance system
    Single-lane entrances
    Two-lane entrances
    Left-hand entrance
  • Lane reduction after an entrance
  • Entrance on a slip road or branch 
    Merging entrance to a lane (Eb 11) 
    Entrance adding two single-lane slip roads (Eb 11) 
  • Entrance system geometry

6 - Geometry of Diverge and Merge Segments 

  • Definitions*
  • Construction of the diverge segment
    Grade-separated interchange between a motorway and an ordinary road*
    Exit to a collector lane
    Loop exit
  • Merge segments
    Grade-separated interchange between a motorway and an ordinary road*
    Merge from a collector lane
  • Crossfall of diverge/merge segments*
  • Markings for diverge/merge segments
    Entrance handled by merging or adding one or two lanes

7 - Closely-Spaced Access Points 

  • 7.1 - Consecutive exits 
    Siting conditions 
    Two exit tapers
    Exit taper followed by a lane assignment exit 
    Lane assignment exit followed by an exit taper 
  • Consecutive entrances* 
  • Entrance followed by an exit
    Direct sequence
    Sequence with a weaving lane
    Sequence with a weaving system on a collector lane* 
  • Connections to the Ordinary Road Network 
  • Developments involving Existing Infrastructure 
    General provisions
    Branch geometry* 
  • Bibliography*
  • Glossary* 


*: updated in 2021

Motorway Interchanges
Numéro ISBN
Catégorie de produit
Nombre de pages
64 pages
Numéro ISSN
Date de parution
Nombre de pages
64 pages
Langue de la publication
Type d'auteur
Oeuvre collective