Preparatory Survey for National Road No.5 Improvement Project (Middle Section: Thlea Ma’am – Battambang, and Sri Sophorn – Poipet) CHAPTER 8 HIGHWAY DESIGN 8.1 Sections for Highway Design Many locations between Thlea M’am and Battambang as well as between Sri Sophorn and Poitet were inundated during the flood which occurred in 2013 and the pavements of these sections were severely damaged. To prevent inundation due to flood and subsequent failure of pavement, height of road surface needs to be set sufficiently higher than the flood water level (see Subsection 8.2.5 for explanation on height of road surface and flood water level). Thus, Thlea Ma’am – Battambang Section and Sri Sophorn – Poipet Section are divided into following 6 sections for the purpose of highway design with regard to flood: Thlea Ma’am – Battambang Section Design Section 1 (KP 171 – KP 138): Flood water level is lower than the existing road surface by 50 cm or more. Thus, the new pavement is constructed on top of the existing pavement. Design Section 2 (KP 183 – KP 190: Pursat Bypass): The bypass is newly constructed traversing mainly agricultural land. The level of flood water is not high. Design Section 3 (KP 190 – KP 255): Flood water level is low and basic concept of design is same to that of Design Section 1 Design Section 4 (KP 255 – KP 283): Flood water level exceeded road surface during the flood in 2013. Height of the new road surface is planned so that the bottom of the pavement structure becomes 50 cm above the recorded flood water level. Sri Sophorn – Poipet Section Design Section 5 (KP 366 – KP 371): Flood water level exceeded road surface during the flood in 2013. The design policy same as that of Design Section 4 is adopted. Design Section 6 (KP 371 – KP 402): Flood water level is low. The new pavement is constructed on top of the existing pavement utilizing the existing pavement as the subgrade. Figure 8.1-1 Design Sections Final Report 8-1 Preparatory Survey for National Road No.5 Improvement Project (Middle Section: Thlea Ma’am – Battambang, and Sri Sophorn – Poipet) Final Report 8-2 Preparatory Survey for National Road No.5 Improvement Project (Middle Section: Thlea Ma’am – Battambang, and Sri Sophorn – Poipet) Figure 8.1-2 Typical Cross Sections on the Middle Section and Sri Sophorn – Poipet Section 8.2 Middle Section 8.2.1 Basic Design Policy and Design Criteria The design of the North Section (Battambang – Sri Sophorn) and the South Section (Prek Kdam – Thlea Ma’am) of NR 5 were studied in the reports of previous preparatory surveys for these sections. Such design includes the preliminary design for the improvement of NR 5 and construction of four bypasses (Odongk, Kampong Chhnang, Battambang, and Sri Sophorn). Since the Middle Section and Sri Sophorn - Poipet Section are the remaining parts of NR 5, the design policy for the these sections should be consistent with those of other sections. NR 5 is designated as a Class I Road in the hierarchy of the Asian Highway Network. Thus, it is desirable to satisfy the design criteria of Asian Highway Class I Road. At the same time, NR 5 is an arterial national road of Cambodia and it needs to satisfy the Road Design Standard of Cambodia. Table 8.2-1 compares the design criteria of Asian Highway Class I and Road Design Standard of Cambodia. The table also shows the criteria recommended for the Project. These recommended criteria have been discussed and agreed between MPWT and the JICA Team during the Survey of North section. Final Report 8-3 Preparatory Survey for National Road No.5 Improvement Project (Middle Section: Thlea Ma’am – Battambang, and Sri Sophorn – Poipet) Table 8.2-1 Comparison of Design Speed and Criteria Standard Asian Highway Cambodian Standard Recommended Road Class Class I R5 (Rural) U5 (Urban) Rural Urban Design Speed 100 km/h (Flat) 100 km/h (flat) 50 km/h (Type3) 100 km/h 50 km/h Min. Curve Radius 350 m 415 m 90 m 350 m 80 m (Super elevation) (10%) (6%) (6%) (10%) (10%) 8.2.2 Urban Sections At present, the maximum speed on the urban section of NR 5 is regulated to be 40 km/h. Nevertheless, the design speed of 50 km/h is proposed for the urban section, considering the fact that many vehicles travel at 50 km/h or higher. Table 8.2-2 lists the urban sections where the speed is currently regulated at 40 km/h. Design speed of 50 km/h is applied to these sections. Table 8.2-2 List of Urban Sections with Design Speed of 50 km/h is Applied KP Length Name of Location KP 184+100 ~ KP 188+200 4,100 m Pursat KP 197+500 ~ KP 198+300 800 m Andoung Krasang KP 200+800 ~ KP 202+500 1,700 m Bakan KP 208+100 ~ KP 212+700 4,600 m Boeung Khnar KP 215+100 ~ KP 217+000 1,900 m Ou Ta Paong KP 218+800 ~ KP 220+000 1,200 m Svay Daun Keo KP 222+400 ~ KP 224+900 2,500 m Pray Svay KP 230+600 ~ KP 231+600 1,000 m Kalaom Phluk KP 235+900 ~ KP 237+000 1,100 m Pray Svay KP 243+700 ~ KP 245+600 1,900 m Moung Russei 8.2.3 Cross Section Table 8.2-3 compares the design criteria of cross-sectional composition of Asian Highway and the design standard of Cambodia. Table 8.2-3 Comparison of Design Criteria of Cross-Sectional Composition Items Asian Highway Cambodian Standard Recommend Road Class Class I R5 (Rural) U5 (Urban) Lane Width 3.50 m 3.50 m 3.50 m Shoulder Width 3.00 m (Flat) 3.00 m (Flat) 2.50 m (Type3) 3.00 m Median Strip 3.00 m (Flat) 4.0 ~ 12.0 m (Flat) 2.0 ~ 4.0 m (Type3) 3.0 m Cross Slope 2.0% (AC) 2.5 ~ 3.0% (AC) 2.0% Shoulder Slope 3.0 ~ 6.0% 3 ~ 4% (sealed) 3% Vertical Clearance 4.5 m 4.5 m As discussed in Chapter 7, it is proposed that the existing NR 5 to be widened to 4 lanes. From viewpoint of consistency of design standard, it is recommended that the cross section adopted in the North and South Sections be adopted also in the Middle Section. In the North and South Sections, two types of cross section were adopted depending on the roadside land use; rural area Final Report 8-4 Preparatory Survey for National Road No.5 Improvement Project (Middle Section: Thlea Ma’am – Battambang, and Sri Sophorn – Poipet) and urbanized area. With regard to the structure of median strip, raised type median is recommended from the view point of traffic safety. Considerations as mentioned below shall be given for convenience of road user in the detail design stage: Opening of median division for left-turn and u-turn should be provided at regular interval and at necessary place. U-turn lane shall be provided at a regular interval and at necessary locations. Figure 8.2-1 shows the proposed typical cross sections for rural area and urbanized area. For the sections passing through urbanized areas where many vehicles are anticipated to park on the street, a 2.5 m-wide parking spaces is proposed on both sides. CL 23000 3000 3500 3500 3000 3500 3500 3000 Shoulder CarriageWay Median CarriageWay Shoulder General Section (Rural area) CL 28000 3000 2500 3500 3500 3000 3500 3500 2500 3000 Sidewalk Parking Zone CarriageWay Median CarriageWay Parking Zone Sidewalk Drain Pipe Drain Pipe Urban Section (Commercial area) Figure 8.2-1 Typical Cross Section 8.2.4 Horizontal Alignment The horizontal alignment of the Middle Section of NR 5 is mostly composed of long straight sections connected each other by relatively short curve sections. These curves sections need to be improved if the existing configurations do not satisfy the requirements of design criteria. (1) Existing Horizontal Alignment There are 41 curve sections and 125 bending points with small intersecting angles without curve between the straight lines along the Middle Section. The radii of many curves are generally small and some of them do not satisfy the requirement of design criteria. In addition, there are some curve sections where the lengths of curve are too short to meet the design criteria. In such short curves, the drivers are confused and, are forced quick steering operation. These short curve sections and many bending points need to be improved by introducing proper lengths of curves. Final Report 8-5 Preparatory Survey for National Road No.5 Improvement Project (Middle Section: Thlea Ma’am – Battambang, and Sri Sophorn – Poipet) (2) Improvement of Horizontal Alignment (a) Small radius of curve There are 6 curve sections where the existing curve radii are smaller than the minimum value defined in the design criteria. Table 8.2-4 shows the curve sections with substandard curve radii and proposed curve radii after improvement. The table also shows the distances of centerline shift due to the improvement. Examples of the improvements of curve sections are shown in Figures 8.2-2 and 8.2-3. (b) Section with short curve length There are 25 curve sections where the existing curve length is insufficient. The lengths of these curve sections are planned to be extended by introducing road sections with larger curve radii. Minimum curve lengths of 170 m and 80 m are achieved for design speed of 100 km/h (general section) and 50 km/h (urban section), respectively.