6. Figure 2 is a part of the HZ district map. A river runs through the district, with the two banks being the broken lines $A-B-C$ and $D-O-E$, and there are two locations $M$ and $N$. Two bridges perpendicular to the riverbanks and roads are to be built to connect $M$ and $N$ to both banks of the river, making the total bridge and road length between $M$ and $N$ the shortest. If
$$
\begin{array}{l}
A(3,15), B(3,3), C(15,3), D(0,15), \\
E(15,0), M(-16,12), N(11,-1),
\end{array}
$$
then the minimum total bridge and road length between $M$ and $N$ is ( ).
(A) 33
(B) 32
(C) 31
(D) 30
6. B.

Translate point $M(-16,12)$ 3 units to the left to get point $M^{\prime}(-13,12)$, and translate point $N(11,-1)$ 3 units upwards to get point $N^{\prime}(11,2)$. Connect $M^{\prime} N^{\prime}$, which intersects $A B$ and $B C$ at points $P$ and $Q$ respectively.
Then the minimum length of the road is
$$
M^{\prime} N^{\prime}=\sqrt{(-13-11)^{2}+(12-2)^{2}}=26 \text {. }
$$

Therefore, the minimum length of the bridge road between $M$ and $N$ is
$$
M^{\prime} N^{\prime}+3+3=26+6=32 \text {. }
$$

The minimum value is achieved when bridges are built at points $P$ and $Q$.