Line detection problem

I am trying to identify lines in a image using hough transform. Problem is that my lines have finite thickness and edge detection identifies each line as two closely spaced parallel lines.

Original Image : http://img43.imageshack.us/i/dislocations.jpg/

Detected lines : http://img219.imageshack.us/i/hough1.jpg/ You can notice that each line has been detected as two parallel lines.

Overlapped : http://img3.imageshack.us/i/hough2.jpg/

Am I taking the right approach? I need to calculate the total length of all those lines in the original image.

The code:

    clear all;
  I  = rgb2gray(imread('dislocations.jpg'));
  BW = edge(I,'sobel');
  figure, imshow(BW);
  [H,theta,rho] = hough(BW,'RhoResolution',1,'ThetaResolution',1);
  figure, imshow(imadjust(mat2gray(H)),[],'XData',theta,'YData',rho,...
          'InitialMagnification','fit');
  xlabel('\theta (degrees)'), ylabel('\rho');
  axis on, axis normal, hold on;
  colormap(hot)
  P = houghpeaks(H,50,'threshold',ceil(0.2*max(H(:))));
  x = theta(P(:,2));
  y = rho(P(:,1));
  plot(x,y,'s','color','black');
  lines = houghlines(BW,theta,rho,P,'FillGap',5,'MinLength',5);
  figure, imshow(I), hold on
  max_len = 0;
  totlen = 0;
  for k = 1:length(lines)
     xy = [lines(k).point1; lines(k).point2];
     plot(xy(:,1),xy(:,2),'LineWidth',1,'Color','green');

     % Plot beginnings and ends of lines
     plot(xy(1,1),xy(1,2),'x','LineWidth',1,'Color','yellow');
     plot(xy(2,1),xy(2,2),'x','LineWidth',1,'Color','red');
     % Determine the endpoints of the longest line segment
     len = norm(lines(k).point1 - lines(k).point2);
     totlen = totlen + len; % total length of lines
  end