For large-diameter municipal sewers, what is the typical maximum spacing adopted between manholes along straight reaches (subject to local codes and access needs)?

Introduction / Context:
Manholes provide access for inspection, cleaning, connection, and ventilation. Spacing depends on pipe size, equipment reach, and alignment geometry, with larger sewers allowing longer spacing.

Given Data / Assumptions:

• Straight alignments without junctions or gradient changes.
• Large-diameter gravity sewers (not small house laterals).
• Typical standards used in many municipalities.

Concept / Approach:

Rules of thumb: small sewers 80–120 m, medium up to ~150–200 m, and large trunks up to ~300 m depending on cleaning technology and safety. Hence a maximum of about 300 m is commonly cited for large sewers, barring bends, junctions, or slope changes which require closer spacing.

Step-by-Step Solution:

Verification / Alternative check:

Many design guides list 250–300 m maxima for trunks, aligning with jetting and CCTV ranges.

Why Other Options Are Wrong:

50–200 m are typical for smaller pipes or constrained sites; 400 m often exceeds accepted access limits for maintenance and safety.

Common Pitfalls:

Ignoring the need for manholes at grade breaks, changes in diameter, junctions, or at every bend; overextending spacing beyond cleaning equipment capability.

Final Answer:

300 m