why hough can't detect the lane line

I try to use hough to detect the line , the right line was missing. how to solve it?

see the result

the hough detect result

code is as following

grapy_pic=rgb2gray(pic);

edge_pic=edge(grapy_pic,'canny',[0.05 0.35]);

imshow(edge_pic)

shape=size(pic);

% row coordinate

a=[shape(2)*0 shape(2)*1 shape(2)*1 0];

%column corordinate

b=[shape(1)*0.05 shape(1)*0.05 shape(1)*0.65 shape(1)*0.65 ];

%use a,b to specify the interesting area

bw=roipoly(pic,a,b);

BW=(edge_pic(:,:,1) & bw);

imshow(BW)

hold on

plot(a, b)

hold off

[H, T, R]=hough(BW') %,'RhoResolution', 1, 'ThetaResolution', 1);

P=houghpeaks(H,5);%'threshold');%,ceil(0.6*max(H(:))));

lines=houghlines(BW,T,R,P,'FillGap',4,'MinLength',5);

imagesc(pic);

hold on;

%plot(lines(5).point1(1),lines(5).point1(2),'rd')

for i=1:length(lines)

plot([lines(i).point1(1),lines(i).point2(1)],[lines(i).point1(2),lines(i).point2(2)],'Color','blue','LineWidth',4)

end

hold off